diff --git a/esphome/components/mdns/mdns_component.cpp b/esphome/components/mdns/mdns_component.cpp
index 8b93c486a7..47db92610a 100644
--- a/esphome/components/mdns/mdns_component.cpp
+++ b/esphome/components/mdns/mdns_component.cpp
@@ -35,7 +35,7 @@ MDNS_STATIC_CONST_CHAR(SERVICE_TCP, "_tcp");
 // Wrap build-time defines into flash storage
 MDNS_STATIC_CONST_CHAR(VALUE_VERSION, ESPHOME_VERSION);
 
-void MDNSComponent::compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUNT> &services) {
+void MDNSComponent::compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUNT> &services, char *mac_address_buf) {
   // IMPORTANT: The #ifdef blocks below must match COMPONENTS_WITH_MDNS_SERVICES
   // in mdns/__init__.py. If you add a new service here, update both locations.
 
@@ -86,7 +86,9 @@ void MDNSComponent::compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUN
       txt_records.push_back({MDNS_STR(TXT_FRIENDLY_NAME), MDNS_STR(friendly_name.c_str())});
     }
     txt_records.push_back({MDNS_STR(TXT_VERSION), MDNS_STR(VALUE_VERSION)});
-    txt_records.push_back({MDNS_STR(TXT_MAC), MDNS_STR(this->mac_address_)});
+
+    // MAC address: passed from caller (either member buffer or stack buffer depending on USE_MDNS_STORE_SERVICES)
+    txt_records.push_back({MDNS_STR(TXT_MAC), MDNS_STR(mac_address_buf)});
 
 #ifdef USE_ESP8266
     MDNS_STATIC_CONST_CHAR(PLATFORM_ESP8266, "ESP8266");
diff --git a/esphome/components/mdns/mdns_component.h b/esphome/components/mdns/mdns_component.h
index 198d1f23ae..d0659abdbf 100644
--- a/esphome/components/mdns/mdns_component.h
+++ b/esphome/components/mdns/mdns_component.h
@@ -70,14 +70,15 @@ class MDNSComponent : public Component {
 
  protected:
   /// Common setup logic called by all platform-specific setup() implementations
-  void on_setup_() {
-#ifdef USE_API
-    // Populate MAC address buffer once during setup
-    get_mac_address_into_buffer(std::span<char, 13>(this->mac_address_));
-#endif
-
+  void on_setup_(char *mac_address_buf) {
 #ifdef USE_MDNS_STORE_SERVICES
-    this->compile_records_(this->services_);
+#ifdef USE_API
+    // Copy to member buffer for storage
+    std::memcpy(this->mac_address_, mac_address_buf, MAC_ADDRESS_BUFFER_SIZE);
+    this->compile_records_(this->services_, this->mac_address_);
+#else
+    this->compile_records_(this->services_, mac_address_buf);
+#endif
 #endif
   }
 
@@ -88,14 +89,14 @@ class MDNSComponent : public Component {
   StaticVector<std::string, MDNS_DYNAMIC_TXT_COUNT> dynamic_txt_values_;
 #endif
 
-#ifdef USE_API
-  /// Fixed buffer for MAC address (populated once in setup())
-  char mac_address_[13];  // 12 hex chars + null terminator
+#if defined(USE_API) && defined(USE_MDNS_STORE_SERVICES)
+  /// Fixed buffer for MAC address (only needed when services are stored)
+  char mac_address_[MAC_ADDRESS_BUFFER_SIZE];
 #endif
 #ifdef USE_MDNS_STORE_SERVICES
   StaticVector<MDNSService, MDNS_SERVICE_COUNT> services_{};
 #endif
-  void compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUNT> &services);
+  void compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUNT> &services, char *mac_address_buf);
 };
 
 }  // namespace esphome::mdns
diff --git a/esphome/components/mdns/mdns_esp32.cpp b/esphome/components/mdns/mdns_esp32.cpp
index 1090ef53b5..4dfb416249 100644
--- a/esphome/components/mdns/mdns_esp32.cpp
+++ b/esphome/components/mdns/mdns_esp32.cpp
@@ -12,13 +12,20 @@ namespace esphome::mdns {
 static const char *const TAG = "mdns";
 
 void MDNSComponent::setup() {
-  this->on_setup_();
+#ifdef USE_API
+  char mac_address[MAC_ADDRESS_BUFFER_SIZE];
+  get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE>(mac_address));
+#else
+  char *mac_address = nullptr;
+#endif
+
+  this->on_setup_(mac_address);
 
 #ifdef USE_MDNS_STORE_SERVICES
   const auto &services = this->services_;
 #else
   StaticVector<MDNSService, MDNS_SERVICE_COUNT> services;
-  this->compile_records_(services);
+  this->compile_records_(services, mac_address);
 #endif
 
   esp_err_t err = mdns_init();
diff --git a/esphome/components/mdns/mdns_esp8266.cpp b/esphome/components/mdns/mdns_esp8266.cpp
index 14ba355f4a..e70028d075 100644
--- a/esphome/components/mdns/mdns_esp8266.cpp
+++ b/esphome/components/mdns/mdns_esp8266.cpp
@@ -12,13 +12,20 @@
 namespace esphome::mdns {
 
 void MDNSComponent::setup() {
-  this->on_setup_();
+#ifdef USE_API
+  char mac_address[MAC_ADDRESS_BUFFER_SIZE];
+  get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE>(mac_address));
+#else
+  char *mac_address = nullptr;
+#endif
+
+  this->on_setup_(mac_address);
 
 #ifdef USE_MDNS_STORE_SERVICES
   const auto &services = this->services_;
 #else
   StaticVector<MDNSService, MDNS_SERVICE_COUNT> services;
-  this->compile_records_(services);
+  this->compile_records_(services, mac_address);
 #endif
 
   MDNS.begin(App.get_name().c_str());
diff --git a/esphome/components/mdns/mdns_host.cpp b/esphome/components/mdns/mdns_host.cpp
index c154b44049..1be0b721c5 100644
--- a/esphome/components/mdns/mdns_host.cpp
+++ b/esphome/components/mdns/mdns_host.cpp
@@ -9,7 +9,14 @@
 namespace esphome::mdns {
 
 void MDNSComponent::setup() {
-  this->on_setup_();
+#ifdef USE_API
+  char mac_address[MAC_ADDRESS_BUFFER_SIZE];
+  get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE>(mac_address));
+#else
+  char *mac_address = nullptr;
+#endif
+
+  this->on_setup_(mac_address);
   // Host platform doesn't have actual mDNS implementation
 }
 
diff --git a/esphome/components/mdns/mdns_libretiny.cpp b/esphome/components/mdns/mdns_libretiny.cpp
index 2ee162ac2e..04c6f8f89d 100644
--- a/esphome/components/mdns/mdns_libretiny.cpp
+++ b/esphome/components/mdns/mdns_libretiny.cpp
@@ -12,13 +12,20 @@
 namespace esphome::mdns {
 
 void MDNSComponent::setup() {
-  this->on_setup_();
+#ifdef USE_API
+  char mac_address[MAC_ADDRESS_BUFFER_SIZE];
+  get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE>(mac_address));
+#else
+  char *mac_address = nullptr;
+#endif
+
+  this->on_setup_(mac_address);
 
 #ifdef USE_MDNS_STORE_SERVICES
   const auto &services = this->services_;
 #else
   StaticVector<MDNSService, MDNS_SERVICE_COUNT> services;
-  this->compile_records_(services);
+  this->compile_records_(services, mac_address);
 #endif
 
   MDNS.begin(App.get_name().c_str());
diff --git a/esphome/components/mdns/mdns_rp2040.cpp b/esphome/components/mdns/mdns_rp2040.cpp
index 102e9eb3c2..10677b49ed 100644
--- a/esphome/components/mdns/mdns_rp2040.cpp
+++ b/esphome/components/mdns/mdns_rp2040.cpp
@@ -12,13 +12,20 @@
 namespace esphome::mdns {
 
 void MDNSComponent::setup() {
-  this->on_setup_();
+#ifdef USE_API
+  char mac_address[MAC_ADDRESS_BUFFER_SIZE];
+  get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE>(mac_address));
+#else
+  char *mac_address = nullptr;
+#endif
+
+  this->on_setup_(mac_address);
 
 #ifdef USE_MDNS_STORE_SERVICES
   const auto &services = this->services_;
 #else
   StaticVector<MDNSService, MDNS_SERVICE_COUNT> services;
-  this->compile_records_(services);
+  this->compile_records_(services, mac_address);
 #endif
 
   MDNS.begin(App.get_name().c_str());
diff --git a/esphome/core/helpers.cpp b/esphome/core/helpers.cpp
index 38efce1187..5e6e637a1d 100644
--- a/esphome/core/helpers.cpp
+++ b/esphome/core/helpers.cpp
@@ -640,17 +640,17 @@ std::string get_mac_address() {
 }
 
 std::string get_mac_address_pretty() {
-  char buf[18];
+  char buf[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
   return std::string(get_mac_address_pretty_into_buffer(buf));
 }
 
-void get_mac_address_into_buffer(std::span<char, 13> buf) {
+void get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE> buf) {
   uint8_t mac[6];
   get_mac_address_raw(mac);
   format_mac_addr_lower_no_sep(mac, buf.data());
 }
 
-const char *get_mac_address_pretty_into_buffer(std::span<char, 18> buf) {
+const char *get_mac_address_pretty_into_buffer(std::span<char, MAC_ADDRESS_PRETTY_BUFFER_SIZE> buf) {
   uint8_t mac[6];
   get_mac_address_raw(mac);
   format_mac_addr_upper(mac, buf.data());
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index d3bec31efa..79e537153e 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -1123,6 +1123,12 @@ class HighFrequencyLoopRequester {
 /// Get the device MAC address as raw bytes, written into the provided byte array (6 bytes).
 void get_mac_address_raw(uint8_t *mac);  // NOLINT(readability-non-const-parameter)
 
+/// Buffer size for MAC address in lowercase hex notation (12 hex chars + null terminator)
+constexpr size_t MAC_ADDRESS_BUFFER_SIZE = 13;
+
+/// Buffer size for MAC address in colon-separated uppercase hex notation (17 chars + null terminator)
+constexpr size_t MAC_ADDRESS_PRETTY_BUFFER_SIZE = 18;
+
 /// Get the device MAC address as a string, in lowercase hex notation.
 std::string get_mac_address();
 
@@ -1130,13 +1136,14 @@ std::string get_mac_address();
 std::string get_mac_address_pretty();
 
 /// Get the device MAC address into the given buffer, in lowercase hex notation.
-/// Assumes buffer length is 13 (12 digits for hexadecimal representation followed by null terminator).
-void get_mac_address_into_buffer(std::span<char, 13> buf);
+/// Assumes buffer length is MAC_ADDRESS_BUFFER_SIZE (12 digits for hexadecimal representation followed by null
+/// terminator).
+void get_mac_address_into_buffer(std::span<char, MAC_ADDRESS_BUFFER_SIZE> buf);
 
 /// Get the device MAC address into the given buffer, in colon-separated uppercase hex notation.
-/// Buffer must be exactly 18 bytes (17 for "XX:XX:XX:XX:XX:XX" + null terminator).
+/// Buffer must be exactly MAC_ADDRESS_PRETTY_BUFFER_SIZE bytes (17 for "XX:XX:XX:XX:XX:XX" + null terminator).
 /// Returns pointer to the buffer for convenience.
-const char *get_mac_address_pretty_into_buffer(std::span<char, 18> buf);
+const char *get_mac_address_pretty_into_buffer(std::span<char, MAC_ADDRESS_PRETTY_BUFFER_SIZE> buf);
 
 #ifdef USE_ESP32
 /// Set the MAC address to use from the provided byte array (6 bytes).