diff --git a/rclcpp/include/rclcpp/experimental/intra_process_manager.hpp b/rclcpp/include/rclcpp/experimental/intra_process_manager.hpp
index a403c20c8b..51b0445324 100644
--- a/rclcpp/include/rclcpp/experimental/intra_process_manager.hpp
+++ b/rclcpp/include/rclcpp/experimental/intra_process_manager.hpp
@@ -19,6 +19,7 @@
 
 #include <shared_mutex>
 
+#include <algorithm>
 #include <iterator>
 #include <memory>
 #include <stdexcept>
@@ -386,6 +387,39 @@ class IntraProcessManager
     std::vector<uint64_t> take_ownership_subscriptions;
   };
 
+  /// Hash function for rmw_gid_t to enable use in unordered_map
+  struct rmw_gid_hash
+  {
+    std::size_t operator()(const rmw_gid_t & gid) const noexcept
+    {
+      // Using the FNV-1a hash algorithm on the gid data
+      constexpr std::size_t FNV_prime = 1099511628211u;
+      std::size_t result = 14695981039346656037u;
+
+      for (std::size_t i = 0; i < RMW_GID_STORAGE_SIZE; ++i) {
+        result ^= gid.data[i];
+        result *= FNV_prime;
+      }
+      return result;
+    }
+  };
+
+  /// Equality comparison for rmw_gid_t to enable use in unordered_map
+  struct rmw_gid_equal
+  {
+    bool operator()(const rmw_gid_t & lhs, const rmw_gid_t & rhs) const noexcept
+    {
+      // Compare the data bytes only.
+      // implementation_identifier pointer comparison is not used here because
+      // intra-process communication is always within the same process and RMW,
+      // and pointer comparison is fragile across dynamically loaded components.
+      return std::equal(
+        std::begin(lhs.data),
+        std::end(lhs.data),
+        std::begin(rhs.data));
+    }
+  };
+
   using SubscriptionMap =
     std::unordered_map<uint64_t, rclcpp::experimental::SubscriptionIntraProcessBase::WeakPtr>;
 
@@ -398,6 +432,16 @@ class IntraProcessManager
   using PublisherToSubscriptionIdsMap =
     std::unordered_map<uint64_t, SplittedSubscriptions>;
 
+  /// Structure to store publisher information in GID lookup map
+  struct PublisherInfo
+  {
+    uint64_t pub_id;
+    rclcpp::PublisherBase::WeakPtr publisher;
+  };
+
+  using GidToPublisherInfoMap =
+    std::unordered_map<rmw_gid_t, PublisherInfo, rmw_gid_hash, rmw_gid_equal>;
+
   RCLCPP_PUBLIC
   static
   uint64_t
@@ -642,6 +686,8 @@ class IntraProcessManager
   PublisherBufferMap publisher_buffers_;
 
   mutable std::shared_timed_mutex mutex_;
+
+  GidToPublisherInfoMap gid_to_publisher_info_;
 };
 
 }  // namespace experimental
diff --git a/rclcpp/src/rclcpp/intra_process_manager.cpp b/rclcpp/src/rclcpp/intra_process_manager.cpp
index 831ffdf2ca..f7bc6fa9b3 100644
--- a/rclcpp/src/rclcpp/intra_process_manager.cpp
+++ b/rclcpp/src/rclcpp/intra_process_manager.cpp
@@ -51,6 +51,9 @@ IntraProcessManager::add_publisher(
     }
   }
 
+  // Add GID to publisher info mapping for fast lookups (stores both ID and weak_ptr)
+  gid_to_publisher_info_[publisher->get_gid()] = {pub_id, publisher};
+
   // Initialize the subscriptions storage for this publisher.
   pub_to_subs_[pub_id] = SplittedSubscriptions();
 
@@ -98,6 +101,24 @@ IntraProcessManager::remove_publisher(uint64_t intra_process_publisher_id)
 {
   std::unique_lock<std::shared_timed_mutex> lock(mutex_);
 
+  // Remove GID to publisher info mapping.
+  // First try via the publisher's own GID (fast path).
+  auto pub_it = publishers_.find(intra_process_publisher_id);
+  if (pub_it != publishers_.end()) {
+    auto publisher = pub_it->second.lock();
+    if (publisher) {
+      gid_to_publisher_info_.erase(publisher->get_gid());
+    } else {
+      // Publisher weak_ptr already expired, fall back to linear scan by pub_id.
+      for (auto git = gid_to_publisher_info_.begin(); git != gid_to_publisher_info_.end(); ++git) {
+        if (git->second.pub_id == intra_process_publisher_id) {
+          gid_to_publisher_info_.erase(git);
+          break;
+        }
+      }
+    }
+  }
+
   publishers_.erase(intra_process_publisher_id);
   publisher_buffers_.erase(intra_process_publisher_id);
   pub_to_subs_.erase(intra_process_publisher_id);
@@ -108,16 +129,15 @@ IntraProcessManager::matches_any_publishers(const rmw_gid_t * id) const
 {
   std::shared_lock<std::shared_timed_mutex> lock(mutex_);
 
-  for (auto & publisher_pair : publishers_) {
-    auto publisher = publisher_pair.second.lock();
-    if (!publisher) {
-      continue;
-    }
-    if (*publisher.get() == id) {
-      return true;
-    }
+  // Single O(1) hash map lookup - struct contains both ID and weak_ptr
+  auto it = gid_to_publisher_info_.find(*id);
+  if (it == gid_to_publisher_info_.end()) {
+    return false;
   }
-  return false;
+
+  // Verify the publisher still exists by checking the weak_ptr
+  auto publisher = it->second.publisher.lock();
+  return publisher != nullptr;
 }
 
 size_t
diff --git a/rclcpp/test/rclcpp/test_intra_process_manager.cpp b/rclcpp/test/rclcpp/test_intra_process_manager.cpp
index 5210f6eac0..838b8298b8 100644
--- a/rclcpp/test/rclcpp/test_intra_process_manager.cpp
+++ b/rclcpp/test/rclcpp/test_intra_process_manager.cpp
@@ -162,7 +162,14 @@ class PublisherBase
   explicit PublisherBase(const std::string & topic, const rclcpp::QoS & qos)
   : topic_name(topic),
     qos_profile(qos)
-  {}
+  {
+    // Initialize a mock GID with unique data based on this pointer
+    gid_.implementation_identifier = "mock_rmw";
+    auto ptr_value = reinterpret_cast<std::uintptr_t>(this);
+    for (size_t i = 0; i < RMW_GID_STORAGE_SIZE; ++i) {
+      gid_.data[i] = static_cast<uint8_t>((ptr_value >> (i * 8)) & 0xFF);
+    }
+  }
 
   virtual ~PublisherBase()
   {}
@@ -192,6 +199,12 @@ class PublisherBase
     return qos_profile.durability() == rclcpp::DurabilityPolicy::TransientLocal;
   }
 
+  const rmw_gid_t &
+  get_gid() const
+  {
+    return gid_;
+  }
+
   bool
   operator==([[maybe_unused]] const rmw_gid_t & gid) const
   {
@@ -210,6 +223,7 @@ class PublisherBase
 private:
   std::string topic_name;
   rclcpp::QoS qos_profile;
+  rmw_gid_t gid_;
 };
 
 template<typename T, typename Alloc = std::allocator<void>>