diff --git a/esphome/__main__.py b/esphome/__main__.py
index 4059024531..27262355d6 100644
--- a/esphome/__main__.py
+++ b/esphome/__main__.py
@@ -428,6 +428,8 @@ def parse_args(argv):
     parser.add_argument('-q', '--quiet', help="Disable all esphome logs.",
                         action='store_true')
     parser.add_argument('--dashboard', help=argparse.SUPPRESS, action='store_true')
+    parser.add_argument('-s', '--substitution', nargs=2, action='append',
+                        help='Add a substitution', metavar=('key', 'value'))
     parser.add_argument('configuration', help='Your YAML configuration file.', nargs='*')
 
     subparsers = parser.add_subparsers(help='Commands', dest='command')
@@ -532,7 +534,7 @@ def run_esphome(argv):
         CORE.config_path = conf_path
         CORE.dashboard = args.dashboard
 
-        config = read_config()
+        config = read_config(dict(args.substitution) if args.substitution else {})
         if config is None:
             return 1
         CORE.config = config
diff --git a/esphome/components/substitutions/__init__.py b/esphome/components/substitutions/__init__.py
index 292a7bf299..ab99e040d4 100644
--- a/esphome/components/substitutions/__init__.py
+++ b/esphome/components/substitutions/__init__.py
@@ -101,11 +101,15 @@ def _substitute_item(substitutions, item, path):
     return None
 
 
-def do_substitution_pass(config):
-    if CONF_SUBSTITUTIONS not in config:
+def do_substitution_pass(config, command_line_substitutions):
+    if CONF_SUBSTITUTIONS not in config and not command_line_substitutions:
         return
 
     substitutions = config[CONF_SUBSTITUTIONS]
+    if substitutions is None:
+        substitutions = command_line_substitutions
+    elif command_line_substitutions:
+        substitutions = {**substitutions, **command_line_substitutions}
     with cv.prepend_path('substitutions'):
         if not isinstance(substitutions, dict):
             raise cv.Invalid("Substitutions must be a key to value mapping, got {}"
diff --git a/esphome/config.py b/esphome/config.py
index 8d7c622a27..741b4fb04a 100644
--- a/esphome/config.py
+++ b/esphome/config.py
@@ -387,15 +387,15 @@ def recursive_check_replaceme(value):
     return value
 
 
-def validate_config(config):
+def validate_config(config, command_line_substitutions):
     result = Config()
 
     # 1. Load substitutions
     if CONF_SUBSTITUTIONS in config:
-        result[CONF_SUBSTITUTIONS] = config[CONF_SUBSTITUTIONS]
+        result[CONF_SUBSTITUTIONS] = {**config[CONF_SUBSTITUTIONS], **command_line_substitutions}
         result.add_output_path([CONF_SUBSTITUTIONS], CONF_SUBSTITUTIONS)
         try:
-            substitutions.do_substitution_pass(config)
+            substitutions.do_substitution_pass(config, command_line_substitutions)
         except vol.Invalid as err:
             result.add_error(err)
             return result
@@ -656,7 +656,7 @@ class InvalidYAMLError(EsphomeError):
         self.base_exc = base_exc
 
 
-def _load_config():
+def _load_config(command_line_substitutions):
     try:
         config = yaml_util.load_yaml(CORE.config_path)
     except EsphomeError as e:
@@ -664,7 +664,7 @@ def _load_config():
     CORE.raw_config = config
 
     try:
-        result = validate_config(config)
+        result = validate_config(config, command_line_substitutions)
     except EsphomeError:
         raise
     except Exception:
@@ -674,9 +674,9 @@ def _load_config():
     return result
 
 
-def load_config():
+def load_config(command_line_substitutions):
     try:
-        return _load_config()
+        return _load_config(command_line_substitutions)
     except vol.Invalid as err:
         raise EsphomeError(f"Error while parsing config: {err}")
 
@@ -813,10 +813,10 @@ def strip_default_ids(config):
     return config
 
 
-def read_config():
+def read_config(command_line_substitutions):
     _LOGGER.info("Reading configuration %s...", CORE.config_path)
     try:
-        res = load_config()
+        res = load_config(command_line_substitutions)
     except EsphomeError as err:
         _LOGGER.error("Error while reading config: %s", err)
         return None
diff --git a/esphome/vscode.py b/esphome/vscode.py
index e8c0b106f7..8782ed6e5c 100644
--- a/esphome/vscode.py
+++ b/esphome/vscode.py
@@ -66,7 +66,7 @@ def read_config(args):
             CORE.config_path = data['file']
         vs = VSCodeResult()
         try:
-            res = load_config()
+            res = load_config(dict(args.substitution) if args.substitution else {})
         except Exception as err:  # pylint: disable=broad-except
             vs.add_yaml_error(str(err))
         else: