diff --git a/esphome/components/api/proto.cpp b/esphome/components/api/proto.cpp
index 1ca6b702ada..fb229928e5a 100644
--- a/esphome/components/api/proto.cpp
+++ b/esphome/components/api/proto.cpp
@@ -8,6 +8,18 @@ namespace esphome::api {
 
 static const char *const TAG = "api.proto";
 
+uint32_t ProtoSize::varint_slow(uint32_t value) { return varint_wide(value); }
+
+void ProtoWriteBuffer::encode_varint_raw_slow_(uint32_t value) {
+  do {
+    this->debug_check_bounds_(1);
+    *this->pos_++ = static_cast<uint8_t>(value | 0x80);
+    value >>= 7;
+  } while (value > 0x7F);
+  this->debug_check_bounds_(1);
+  *this->pos_++ = static_cast<uint8_t>(value);
+}
+
 #ifdef USE_API_VARINT64
 optional<ProtoVarInt> ProtoVarInt::parse_wide(const uint8_t *buffer, uint32_t len, uint32_t *consumed,
                                               uint32_t result32) {
diff --git a/esphome/components/api/proto.h b/esphome/components/api/proto.h
index bbdd11b29d0..adde0a8a85b 100644
--- a/esphome/components/api/proto.h
+++ b/esphome/components/api/proto.h
@@ -240,14 +240,13 @@ class ProtoWriteBuffer {
   ProtoWriteBuffer(std::vector<uint8_t> *buffer) : buffer_(buffer), pos_(buffer->data() + buffer->size()) {}
   ProtoWriteBuffer(std::vector<uint8_t> *buffer, size_t write_pos)
       : buffer_(buffer), pos_(buffer->data() + write_pos) {}
-  void encode_varint_raw(uint32_t value) {
-    while (value > 0x7F) {
+  inline void ESPHOME_ALWAYS_INLINE encode_varint_raw(uint32_t value) {
+    if (value < 128) [[likely]] {
       this->debug_check_bounds_(1);
-      *this->pos_++ = static_cast<uint8_t>(value | 0x80);
-      value >>= 7;
+      *this->pos_++ = static_cast<uint8_t>(value);
+      return;
     }
-    this->debug_check_bounds_(1);
-    *this->pos_++ = static_cast<uint8_t>(value);
+    this->encode_varint_raw_slow_(value);
   }
   void encode_varint_raw_64(uint64_t value) {
     while (value > 0x7F) {
@@ -378,6 +377,9 @@ class ProtoWriteBuffer {
   std::vector<uint8_t> *get_buffer() const { return buffer_; }
 
  protected:
+  // Slow path for encode_varint_raw values >= 128, outlined to keep fast path small
+  void encode_varint_raw_slow_(uint32_t value) __attribute__((noinline));
+
 #ifdef ESPHOME_DEBUG_API
   void debug_check_bounds_(size_t bytes, const char *caller = __builtin_FUNCTION());
   void debug_check_encode_size_(uint32_t field_id, uint32_t expected, ptrdiff_t actual);
@@ -511,24 +513,29 @@ class ProtoSize {
    * @param value The uint32_t value to calculate size for
    * @return The number of bytes needed to encode the value
    */
-  static constexpr uint32_t varint(uint32_t value) {
-    // Optimized varint size calculation using leading zeros
-    // Each 7 bits requires one byte in the varint encoding
-    if (value < 128)
-      return 1;  // 7 bits, common case for small values
-
-    // For larger values, count bytes needed based on the position of the highest bit set
-    if (value < 16384) {
-      return 2;  // 14 bits
-    } else if (value < 2097152) {
-      return 3;  // 21 bits
-    } else if (value < 268435456) {
-      return 4;  // 28 bits
-    } else {
-      return 5;  // 32 bits (maximum for uint32_t)
-    }
+  static constexpr inline uint32_t ESPHOME_ALWAYS_INLINE varint(uint32_t value) {
+    if (value < 128) [[likely]]
+      return 1;  // Fast path: 7 bits, most common case
+    if (__builtin_is_constant_evaluated())
+      return varint_wide(value);
+    return varint_slow(value);
   }
 
+ private:
+  // Slow path for varint >= 128, outlined to keep fast path small
+  static uint32_t varint_slow(uint32_t value) __attribute__((noinline));
+  // Shared cascade for values >= 128 (used by both constexpr and noinline paths)
+  static constexpr inline uint32_t ESPHOME_ALWAYS_INLINE varint_wide(uint32_t value) {
+    if (value < 16384)
+      return 2;
+    if (value < 2097152)
+      return 3;
+    if (value < 268435456)
+      return 4;
+    return 5;
+  }
+
+ public:
   /**
    * @brief Calculates the size in bytes needed to encode a uint64_t value as a varint
    *