diff --git a/contract/contracts/hello-world/src/autoshare_logic.rs b/contract/contracts/hello-world/src/autoshare_logic.rs
index b1f78bd..aea970b 100644
--- a/contract/contracts/hello-world/src/autoshare_logic.rs
+++ b/contract/contracts/hello-world/src/autoshare_logic.rs
@@ -1,15 +1,12 @@
 use crate::base::errors::Error;
 use crate::base::events::{
-    AdminTransferred, AuthorizationFailure, AutoshareCreated, AutoshareUpdated, CategoryRegistered,
-    ContractPaused, ContractUnpaused, GroupActivated, GroupDeactivated, NotificationCategory,
-    NotificationDelivered, NotificationExpired, NotificationExtended, NotificationLimitsConfigured,
-    NotificationPriority, NotificationRecalled, NotificationRevoked, NotificationScheduled,
-    ScheduledNotificationCancelled, Withdrawal,
-    AdminTransferred, AuthorizationFailure, AutoshareCreated, AutoshareUpdated, ContractPaused,
-    ContractUnpaused, GroupActivated, GroupDeactivated, NotificationAcknowledged,
-    NotificationCategory, NotificationExpired, NotificationPriority, NotificationRevoked,
-    NotificationScheduled, ScheduledNotificationCancelled, Withdrawal,
     AdminTransferred, AuditAction, AuditRecordAppended, AuthorizationFailure, AutoshareCreated,
+    AutoshareUpdated, BatchNotificationsCreated, BatchProcessingCompleted, CategoryRegistered,
+    ContractPaused, ContractUnpaused, GroupActivated, GroupDeactivated, NotificationAccessed,
+    NotificationAcknowledged, NotificationCategory, NotificationDelivered, NotificationExpired,
+    NotificationExtended, NotificationLimitsConfigured, NotificationPriority, NotificationRecalled,
+    NotificationRevoked, NotificationScheduled, ScheduledNotificationCancelled,
+    SchemaVersionSet, SubscriptionCancelled, Withdrawal,
     AutoshareUpdated, BatchNotificationsCreated, CategoryRegistered, ContractPaused,
     ContractUnpaused, GroupActivated, GroupDeactivated, NotificationCategory, NotificationExpired,
     NotificationPriority, NotificationRevoked, NotificationScheduled, OwnershipTransferInitiated,
@@ -751,6 +748,72 @@ pub fn topup_subscription(
     Ok(())
 }
 
+/// Cancels an active notification subscription for a group and emits a
+/// [`SubscriptionCancelled`] event so off-chain consumers can track the full
+/// subscription lifecycle.
+///
+/// The subscriber must be the group's creator or an authorised member of the
+/// group. Cancellation marks the group as inactive (deactivates it) and zeroes
+/// out the remaining usage count so no further notifications can be dispatched
+/// against the subscription.
+///
+/// # Errors
+/// - [`Error::ContractPaused`]   – the contract is currently paused.
+/// - [`Error::NotFound`]         – `id` does not correspond to a known group.
+/// - [`Error::Unauthorized`]     – `subscriber` is neither the creator nor a
+///                                 member of the group.
+/// - [`Error::GroupInactive`]    – the group is already inactive (subscription
+///                                 already cancelled or never active).
+pub fn cancel_subscription(
+    env: Env,
+    id: BytesN<32>,
+    subscriber: Address,
+) -> Result<(), Error> {
+    subscriber.require_auth();
+
+    if get_paused_status(&env) {
+        return Err(Error::ContractPaused);
+    }
+
+    let key = DataKey::AutoShare(id.clone());
+    let mut details: AutoShareDetails = env
+        .storage()
+        .persistent()
+        .get(&key)
+        .ok_or(Error::NotFound)?;
+
+    // Only the creator or a current member may cancel the subscription.
+    let is_creator = details.creator == subscriber;
+    let is_member = details.members.iter().any(|m| m.address == subscriber);
+
+    if !is_creator && !is_member {
+        publish_authorization_failure(&env, &subscriber, "cancel_subscription");
+        return Err(Error::Unauthorized);
+    }
+
+    if !details.is_active {
+        return Err(Error::GroupInactive);
+    }
+
+    // Deactivate the group and clear remaining usages.
+    details.is_active = false;
+    details.usage_count = 0;
+    env.storage().persistent().set(&key, &details);
+
+    let cancelled_at = env.ledger().timestamp();
+
+    SubscriptionCancelled {
+        group_id: id,
+        subscriber,
+        category: NotificationCategory::Group,
+        priority: NotificationPriority::Medium,
+        cancelled_at,
+    }
+    .publish(&env);
+
+    Ok(())
+}
+
 // ============================================================================
 // Payment History
 // ============================================================================
diff --git a/contract/contracts/hello-world/src/base/events.rs b/contract/contracts/hello-world/src/base/events.rs
index f454f30..cd207d9 100644
--- a/contract/contracts/hello-world/src/base/events.rs
+++ b/contract/contracts/hello-world/src/base/events.rs
@@ -469,6 +469,21 @@ pub struct NotificationAcknowledged {
     pub timestamp: u64,
 }
 
+/// Emitted when a subscriber cancels an active notification subscription.
+///
+/// Off-chain consumers can key off `(group_id, subscriber)` to track the full
+/// subscription lifecycle. The `group_id` identifies the AutoShare group whose
+/// subscription was cancelled; `subscriber` is the address that initiated the
+/// cancellation.
+#[contractevent(data_format = "single-value")]
+#[derive(Clone)]
+pub struct SubscriptionCancelled {
+    /// The group whose subscription was cancelled.
+    #[topic]
+    pub group_id: BytesN<32>,
+    /// The address that cancelled the subscription.
+    #[topic]
+    pub subscriber: Address,
 /// Emitted when the current owner initiates a two-step ownership transfer by
 /// nominating a `pending_owner`. The transfer is not final until the pending
 /// owner calls `accept_ownership`.
@@ -499,5 +514,7 @@ pub struct OwnershipTransferred {
     pub category: NotificationCategory,
     #[topic]
     pub priority: NotificationPriority,
+    /// Ledger timestamp (seconds) when the cancellation occurred.
+    pub cancelled_at: u64,
     pub new_owner: Address,
 }
diff --git a/contract/contracts/hello-world/src/lib.rs b/contract/contracts/hello-world/src/lib.rs
index ebfbaba..f834d9b 100644
--- a/contract/contracts/hello-world/src/lib.rs
+++ b/contract/contracts/hello-world/src/lib.rs
@@ -275,6 +275,16 @@ impl AutoShareContract {
             .unwrap();
     }
 
+    /// Cancels an active notification subscription for a group.
+    ///
+    /// The `subscriber` must be the group's creator or a current member. On
+    /// success the group is deactivated, its remaining usage count is zeroed, and
+    /// a `SubscriptionCancelled` event is emitted so off-chain consumers can
+    /// track the full subscription lifecycle.
+    pub fn cancel_subscription(env: Env, id: BytesN<32>, subscriber: Address) {
+        autoshare_logic::cancel_subscription(env, id, subscriber).unwrap();
+    }
+
     // ============================================================================
     // Payment History
     // ============================================================================
@@ -712,4 +722,7 @@ mod tests {
 
     #[path = "../tests/access_log_test.rs"]
     mod access_log_test;
+
+    #[path = "../tests/subscription_cancellation_test.rs"]
+    mod subscription_cancellation_test;
 }
diff --git a/contract/contracts/hello-world/src/tests/subscription_cancellation_test.rs b/contract/contracts/hello-world/src/tests/subscription_cancellation_test.rs
new file mode 100644
index 0000000..858404b
--- /dev/null
+++ b/contract/contracts/hello-world/src/tests/subscription_cancellation_test.rs
@@ -0,0 +1,342 @@
+//! Tests for issue #375 – Emit Event on Subscription Cancellation.
+//!
+//! Acceptance criteria verified here:
+//! 1. Cancelling an active subscription emits a `subscription_cancelled` event.
+//! 2. The emitted event contains subscriber information (group_id + subscriber
+//!    as indexed topics, cancelled_at as payload data).
+//! 3. Edge cases: non-member cannot cancel, already-inactive group is rejected,
+//!    paused contract blocks cancellation, member (non-creator) can cancel.
+
+use crate::base::errors::Error;
+use crate::base::events::{NotificationCategory, NotificationPriority};
+use crate::test_utils::{create_test_group, setup_test_env};
+use crate::AutoShareContractClient;
+
+use soroban_sdk::testutils::{Address as _, Events};
+use soroban_sdk::{Address, BytesN, Symbol, TryFromVal, Val, Vec};
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+/// Returns the topics of the most recent event whose first topic matches
+/// `event_name`, or `None` if no such event was emitted.
+fn topics_of(env: &soroban_sdk::Env, event_name: &str) -> Option<Vec<Val>> {
+    let target = Symbol::new(env, event_name);
+    let mut found: Option<Vec<Val>> = None;
+    for (_addr, topics, _data) in env.events().all().iter() {
+        if topics.is_empty() {
+            continue;
+        }
+        if let Ok(name) = Symbol::try_from_val(env, &topics.get(0).unwrap()) {
+            if name == target {
+                found = Some(topics);
+            }
+        }
+    }
+    found
+}
+
+/// Returns the raw event data `Val` for the most recent event matching
+/// `event_name`, or `None` if not found.
+fn data_of(env: &soroban_sdk::Env, event_name: &str) -> Option<Val> {
+    let target = Symbol::new(env, event_name);
+    let mut found: Option<Val> = None;
+    for (_addr, topics, data) in env.events().all().iter() {
+        if topics.is_empty() {
+            continue;
+        }
+        if let Ok(name) = Symbol::try_from_val(env, &topics.get(0).unwrap()) {
+            if name == target {
+                found = Some(data);
+            }
+        }
+    }
+    found
+}
+
+// ---------------------------------------------------------------------------
+// AC-1: Cancellation emits a `subscription_cancelled` event
+// ---------------------------------------------------------------------------
+
+#[test]
+fn test_cancel_subscription_emits_event() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        1,
+        &token,
+    );
+
+    client.cancel_subscription(&id, &creator);
+
+    assert!(
+        topics_of(&test_env.env, "subscription_cancelled").is_some(),
+        "expected a subscription_cancelled event to be emitted"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// AC-2: Event contains subscriber information
+// ---------------------------------------------------------------------------
+
+#[test]
+fn test_cancel_subscription_event_topic_shape() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        1,
+        &token,
+    );
+
+    client.cancel_subscription(&id, &creator);
+
+    let topics = topics_of(&test_env.env, "subscription_cancelled")
+        .expect("subscription_cancelled event must be emitted");
+
+    // Expected shape: [event_name, group_id, subscriber, category, priority]
+    assert_eq!(topics.len(), 5, "expected 5 topics on subscription_cancelled");
+
+    // Topic[0]: event name symbol
+    let name = Symbol::try_from_val(&test_env.env, &topics.get(0).unwrap()).unwrap();
+    assert_eq!(name, Symbol::new(&test_env.env, "subscription_cancelled"));
+
+    // Topic[1]: group_id
+    let emitted_id =
+        BytesN::<32>::try_from_val(&test_env.env, &topics.get(1).unwrap()).unwrap();
+    assert_eq!(emitted_id, id);
+
+    // Topic[2]: subscriber address
+    let emitted_subscriber =
+        Address::try_from_val(&test_env.env, &topics.get(2).unwrap()).unwrap();
+    assert_eq!(emitted_subscriber, creator);
+
+    // Topic[3]: category == Group
+    let category =
+        NotificationCategory::try_from_val(&test_env.env, &topics.get(3).unwrap()).unwrap();
+    assert_eq!(category, NotificationCategory::Group);
+
+    // Topic[4]: priority == Medium
+    let priority =
+        NotificationPriority::try_from_val(&test_env.env, &topics.get(4).unwrap()).unwrap();
+    assert_eq!(priority, NotificationPriority::Medium);
+}
+
+#[test]
+fn test_cancel_subscription_event_data_contains_cancelled_at() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        1,
+        &token,
+    );
+
+    client.cancel_subscription(&id, &creator);
+
+    let raw_data = data_of(&test_env.env, "subscription_cancelled")
+        .expect("subscription_cancelled event must be emitted");
+
+    // Data is the `cancelled_at` u64 timestamp.
+    let cancelled_at = u64::try_from_val(&test_env.env, &raw_data).unwrap();
+    // Ledger timestamp in tests defaults to 0; just assert it decodes without panic.
+    let _ = cancelled_at;
+}
+
+// ---------------------------------------------------------------------------
+// AC-2 (extended): Group is deactivated after cancellation
+// ---------------------------------------------------------------------------
+
+#[test]
+fn test_cancel_subscription_deactivates_group() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        5,
+        &token,
+    );
+
+    assert!(client.is_group_active(&id), "group must be active before cancel");
+
+    client.cancel_subscription(&id, &creator);
+
+    assert!(
+        !client.is_group_active(&id),
+        "group must be inactive after cancel"
+    );
+    assert_eq!(
+        client.get_remaining_usages(&id),
+        0,
+        "remaining usages must be zeroed after cancel"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Edge case: non-member / non-creator cannot cancel
+// ---------------------------------------------------------------------------
+
+#[test]
+#[should_panic]
+fn test_cancel_subscription_rejects_non_member() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let outsider = test_env.users.get(1).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        1,
+        &token,
+    );
+
+    // outsider is neither creator nor member – must panic (Unauthorized)
+    client.cancel_subscription(&id, &outsider);
+}
+
+// ---------------------------------------------------------------------------
+// Edge case: already-inactive group is rejected
+// ---------------------------------------------------------------------------
+
+#[test]
+#[should_panic]
+fn test_cancel_subscription_rejects_already_inactive_group() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        1,
+        &token,
+    );
+
+    client.cancel_subscription(&id, &creator);
+    // Second cancellation on an already-inactive group must panic (GroupInactive)
+    client.cancel_subscription(&id, &creator);
+}
+
+// ---------------------------------------------------------------------------
+// Edge case: paused contract blocks cancellation
+// ---------------------------------------------------------------------------
+
+#[test]
+#[should_panic]
+fn test_cancel_subscription_blocked_when_paused() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        1,
+        &token,
+    );
+
+    client.pause(&test_env.admin);
+    // Cancellation while paused must panic (ContractPaused)
+    client.cancel_subscription(&id, &creator);
+}
+
+// ---------------------------------------------------------------------------
+// Edge case: group member (non-creator) can cancel
+// ---------------------------------------------------------------------------
+
+#[test]
+fn test_cancel_subscription_by_member() {
+    use crate::base::types::GroupMember;
+
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let creator = test_env.users.get(0).unwrap().clone();
+    let member_addr = test_env.users.get(1).unwrap().clone();
+    let token = test_env.mock_tokens.get(0).unwrap().clone();
+
+    let id = create_test_group(
+        &test_env.env,
+        &test_env.autoshare_contract,
+        &creator,
+        &Vec::new(&test_env.env),
+        1,
+        &token,
+    );
+
+    // Add member_addr to the group so they are authorised to cancel.
+    let mut members = Vec::new(&test_env.env);
+    members.push_back(GroupMember {
+        address: member_addr.clone(),
+        percentage: 100,
+    });
+    client.update_members(&id, &creator, &members);
+
+    // Member cancels the subscription.
+    client.cancel_subscription(&id, &member_addr);
+
+    assert!(
+        topics_of(&test_env.env, "subscription_cancelled").is_some(),
+        "subscription_cancelled event must be emitted when a member cancels"
+    );
+
+    // Subscriber topic must reflect member_addr, not creator.
+    let topics = topics_of(&test_env.env, "subscription_cancelled").unwrap();
+    let emitted_subscriber =
+        Address::try_from_val(&test_env.env, &topics.get(2).unwrap()).unwrap();
+    assert_eq!(emitted_subscriber, member_addr);
+}
+
+// ---------------------------------------------------------------------------
+// Edge case: unknown group id returns NotFound (panics)
+// ---------------------------------------------------------------------------
+
+#[test]
+#[should_panic]
+fn test_cancel_subscription_unknown_group_panics() {
+    let test_env = setup_test_env();
+    let client = AutoShareContractClient::new(&test_env.env, &test_env.autoshare_contract);
+    let caller = test_env.users.get(0).unwrap().clone();
+
+    let mut id_bytes = [0u8; 32];
+    id_bytes[0] = 0xff;
+    let unknown_id = BytesN::from_array(&test_env.env, &id_bytes);
+
+    // Must panic (NotFound) since the group was never created.
+    client.cancel_subscription(&unknown_id, &caller);
+}