diff --git a/esphome/components/http_request/update/http_request_update.cpp b/esphome/components/http_request/update/http_request_update.cpp
index 57dc86d55cf..6a74c00e8e5 100644
--- a/esphome/components/http_request/update/http_request_update.cpp
+++ b/esphome/components/http_request/update/http_request_update.cpp
@@ -1,5 +1,7 @@
 #include "http_request_update.h"
 
+#include <cstring>
+
 #include "esphome/core/application.h"
 #include "esphome/core/version.h"
 
@@ -94,7 +96,7 @@ void HttpRequestUpdate::update_task(void *params) {
   auto container = this_update->request_parent_->get(this_update->source_url_);
 
   if (container == nullptr || container->status_code != HTTP_STATUS_OK) {
-    ESP_LOGE(TAG, "Failed to fetch manifest from %s", this_update->source_url_.c_str());
+    ESP_LOGE(TAG, "Failed to fetch manifest from %s", this_update->source_url_);
     if (container != nullptr)
       container->end();
     result->error_str = LOG_STR("Failed to fetch manifest");
@@ -174,21 +176,26 @@ void HttpRequestUpdate::update_task(void *params) {
     allocator.deallocate(data, content_length);
 
     if (!valid) {
-      ESP_LOGE(TAG, "Failed to parse JSON from %s", this_update->source_url_.c_str());
+      ESP_LOGE(TAG, "Failed to parse JSON from %s", this_update->source_url_);
       result->error_str = LOG_STR("Failed to parse manifest JSON");
       goto defer;  // NOLINT(cppcoreguidelines-avoid-goto)
     }
 
     // Merge source_url_ and firmware_url
     if (!info->firmware_url.empty() && info->firmware_url.find("http") == std::string::npos) {
-      std::string path = info->firmware_url;
-      if (path[0] == '/') {
-        std::string domain = this_update->source_url_.substr(0, this_update->source_url_.find('/', 8));
-        info->firmware_url = domain + path;
+      const char *source = this_update->source_url_;
+      const size_t source_len = strlen(source);
+      size_t prefix_len;
+      if (info->firmware_url[0] == '/') {
+        // scheme and host, up to the first slash after "https://"
+        const char *host_end = source_len > 8 ? strchr(source + 8, '/') : nullptr;
+        prefix_len = host_end != nullptr ? host_end - source : source_len;
       } else {
-        std::string domain = this_update->source_url_.substr(0, this_update->source_url_.rfind('/') + 1);
-        info->firmware_url = domain + path;
+        // directory of the manifest, up to and including its last slash
+        const char *dir_end = strrchr(source, '/');
+        prefix_len = dir_end != nullptr ? dir_end - source + 1 : 0;
       }
+      info->firmware_url.insert(0, source, prefix_len);
     }
 
 #ifdef ESPHOME_PROJECT_VERSION
diff --git a/esphome/components/http_request/update/http_request_update.h b/esphome/components/http_request/update/http_request_update.h
index be9fbf72bfd..05a741b6cd9 100644
--- a/esphome/components/http_request/update/http_request_update.h
+++ b/esphome/components/http_request/update/http_request_update.h
@@ -21,7 +21,7 @@ class HttpRequestUpdate final : public update::UpdateEntity, public PollingCompo
   void perform(bool force) override;
   void check() override { this->update(); }
 
-  void set_source_url(const std::string &source_url) { this->source_url_ = source_url; }
+  void set_source_url(const char *source_url) { this->source_url_ = source_url; }
 
   void set_request_parent(HttpRequestComponent *request_parent) { this->request_parent_ = request_parent; }
   void set_ota_parent(OtaHttpRequestComponent *ota_parent) { this->ota_parent_ = ota_parent; }
@@ -33,13 +33,15 @@ class HttpRequestUpdate final : public update::UpdateEntity, public PollingCompo
  protected:
   HttpRequestComponent *request_parent_;
   OtaHttpRequestComponent *ota_parent_;
-  std::string source_url_;
 
   static void update_task(void *params);
 #ifdef USE_ESP32
   TaskHandle_t update_task_handle_{nullptr};
 #endif
   uint8_t initial_check_remaining_{0};
+
+ private:
+  const char *source_url_{nullptr};  // literal from codegen
 };
 
 }  // namespace esphome::http_request