diff --git a/src/sources/gcp_cloud_storage/pubsub.rs b/src/sources/gcp_cloud_storage/pubsub.rs
index 83776ce3426cd..6e801d1b86186 100644
--- a/src/sources/gcp_cloud_storage/pubsub.rs
+++ b/src/sources/gcp_cloud_storage/pubsub.rs
@@ -100,6 +100,19 @@ pub struct PubsubConfig {
     #[configurable(metadata(docs::type_unit = "tasks"))]
     #[configurable(metadata(docs::examples = 5))]
     pub client_concurrency: Option<NonZeroUsize>,
+
+    /// The acknowledgement deadline, in seconds, to set for pulled messages.
+    ///
+    /// After pulling a batch, Vector extends the deadline (via `modifyAckDeadline`) to this
+    /// value so that slow processing — including downstream sink batch latency — does not let
+    /// the lease expire and trigger redelivery before the message is acknowledged. This
+    /// decouples processing time from the subscription's static `ackDeadlineSeconds`. Clamped
+    /// to the Pub/Sub-allowed range of 10 to 600 seconds; total processing of a pulled batch
+    /// must complete within this deadline.
+    #[serde(default = "default_ack_deadline_secs")]
+    #[derivative(Default(value = "default_ack_deadline_secs()"))]
+    #[configurable(metadata(docs::type_unit = "seconds"))]
+    pub ack_deadline_secs: u32,
 }
 
 fn default_pubsub_endpoint() -> String {
@@ -114,6 +127,16 @@ const fn default_max_messages() -> u32 {
     10
 }
 
+const fn default_ack_deadline_secs() -> u32 {
+    // Mirror the aws_s3 source's effective visibility timeout (its floor is 600s and the
+    // Pub/Sub maximum is also 600s), so a pulled batch has the same lease behavior.
+    600
+}
+
+/// Bounds for the maintained ack deadline, per the Pub/Sub API.
+const MIN_ACK_DEADLINE_SECS: u32 = 10;
+const MAX_ACK_DEADLINE_SECS: u32 = 600;
+
 const fn default_true() -> bool {
     true
 }
@@ -169,6 +192,12 @@ pub enum ProcessingError {
 
     #[snafu(display("Pub/Sub acknowledge returned HTTP {}: {}", status, body))]
     AcknowledgeMessagesHttp { status: u16, body: String },
+
+    #[snafu(display("Failed to modify Pub/Sub ack deadline: {}", source))]
+    ModifyAckDeadline { source: crate::http::HttpError },
+
+    #[snafu(display("Pub/Sub modifyAckDeadline returned HTTP {}: {}", status, body))]
+    ModifyAckDeadlineHttp { status: u16, body: String },
 }
 
 pub struct State {
@@ -188,6 +217,7 @@ pub struct State {
     client_concurrency: usize,
     delete_message: bool,
     delete_failed_message: bool,
+    ack_deadline_secs: u32,
     decoder: Decoder,
 }
 
@@ -232,6 +262,9 @@ impl Ingestor {
                 .unwrap_or_else(crate::num_threads),
             delete_message: config.delete_message,
             delete_failed_message: config.delete_failed_message,
+            ack_deadline_secs: config
+                .ack_deadline_secs
+                .clamp(MIN_ACK_DEADLINE_SECS, MAX_ACK_DEADLINE_SECS),
             decoder,
         });
 
@@ -353,6 +386,25 @@ impl IngestorProcess {
             return Ok(false);
         }
 
+        // Extend the ack deadline for the whole pulled batch up front (like the aws_s3
+        // source sets its SQS visibility timeout at receive time) so that slow processing —
+        // including downstream sink batch latency — does not let the lease expire and trigger
+        // redelivery before we acknowledge. Best-effort: a failure here is non-fatal; the
+        // message simply retains the subscription's static deadline.
+        if self.state.delete_message {
+            let all_ack_ids: Vec<String> = messages.iter().map(|m| m.ack_id.clone()).collect();
+            if let Err(err) = self
+                .modify_ack_deadline(&all_ack_ids, self.state.ack_deadline_secs)
+                .await
+            {
+                warn!(
+                    message = "Failed to extend Pub/Sub ack deadline; messages may be redelivered.",
+                    %err,
+                    count = all_ack_ids.len(),
+                );
+            }
+        }
+
         let mut ack_ids = Vec::new();
         for message in &messages {
             let message_id = message
@@ -694,6 +746,46 @@ impl IngestorProcess {
         Ok(pull_response.received_messages.unwrap_or_default())
     }
 
+    async fn modify_ack_deadline(
+        &self,
+        ack_ids: &[String],
+        deadline_secs: u32,
+    ) -> Result<(), ProcessingError> {
+        let url = format!(
+            "{}/v1/projects/{}/subscriptions/{}:modifyAckDeadline",
+            self.state.pubsub_endpoint, self.state.project, self.state.subscription
+        );
+
+        let body = serde_json::json!({
+            "ackIds": ack_ids,
+            "ackDeadlineSeconds": deadline_secs,
+        });
+
+        let mut request = http::Request::post(&url)
+            .header("content-type", "application/json")
+            .body(hyper::Body::from(serde_json::to_vec(&body).unwrap()))
+            .expect("building Pub/Sub modifyAckDeadline request should not fail");
+        self.state.auth.apply(&mut request);
+
+        let response = self
+            .state
+            .http_client
+            .send(request)
+            .await
+            .map_err(|source| ProcessingError::ModifyAckDeadline { source })?;
+
+        if !response.status().is_success() {
+            let status = response.status().as_u16();
+            let body_bytes = body_to_bytes(response.into_body())
+                .await
+                .unwrap_or_default();
+            let body = error_body_string(&body_bytes);
+            return Err(ProcessingError::ModifyAckDeadlineHttp { status, body });
+        }
+
+        Ok(())
+    }
+
     async fn acknowledge_messages(&self, ack_ids: &[String]) -> Result<(), ProcessingError> {
         let url = format!(
             "{}/v1/projects/{}/subscriptions/{}:acknowledge",