diff --git a/esphome/core/config.py b/esphome/core/config.py
index 83277321aa..8c130eb6db 100644
--- a/esphome/core/config.py
+++ b/esphome/core/config.py
@@ -113,7 +113,6 @@ else:
 
 
 CONF_ESP8266_RESTORE_FROM_FLASH = "esp8266_restore_from_flash"
-CONF_CUSTOM_PLATFORM = "custom_platform"
 CONFIG_SCHEMA = cv.All(
     cv.Schema(
         {
@@ -168,7 +167,6 @@ CONFIG_SCHEMA = cv.All(
             cv.Optional(
                 CONF_COMPILE_PROCESS_LIMIT, default=_compile_process_limit_default
             ): cv.int_range(min=1, max=multiprocessing.cpu_count()),
-            cv.Optional(CONF_CUSTOM_PLATFORM): cv.string,
         }
     ),
     validate_hostname,
@@ -204,9 +202,6 @@ def preload_core_config(config, result):
         conf[CONF_BUILD_PATH] = os.path.join(build_path, CORE.name)
     CORE.build_path = CORE.relative_internal_path(conf[CONF_BUILD_PATH])
 
-    if conf.get(CONF_CUSTOM_PLATFORM):
-        TARGET_PLATFORMS.extend([conf.get(CONF_CUSTOM_PLATFORM)])
-
     has_oldstyle = CONF_PLATFORM in conf
     newstyle_found = [key for key in TARGET_PLATFORMS if key in config]
     oldstyle_opts = [