diff --git a/esphome/espidf/component.py b/esphome/espidf/component.py
index b1352f7791..7d9874ad5f 100644
--- a/esphome/espidf/component.py
+++ b/esphome/espidf/component.py
@@ -93,7 +93,7 @@ class URLSource(Source):
 
 
 class GitSource(Source):
-    def __init__(self, url: str, ref: str):
+    def __init__(self, url: str, ref: str | None):
         self.url = url
         self.ref = ref
 
@@ -109,7 +109,7 @@ class GitSource(Source):
         return path
 
     def __str__(self):
-        return f"{self.url}#{self.ref}"
+        return f"{self.url}#{self.ref}" if self.ref else self.url
 
 
 class InvalidIDFComponent(Exception):
@@ -352,7 +352,6 @@ def _convert_library_to_component(library: Library) -> IDFComponent:
         IDFComponent: The resolved component with name, version, and URL
 
     Raises:
-        ValueError: If a repository URL is missing a reference (#)
         RuntimeError: If no artifact can be found for the library
     """
     name = None
@@ -362,10 +361,11 @@ def _convert_library_to_component(library: Library) -> IDFComponent:
     #  Repository is provided directly
     if library.repository:
         # Parse repository URL: path becomes the component name, fragment
-        # becomes the git ref stored on GitSource.
+        # (if any) becomes the git ref stored on GitSource. A missing
+        # fragment is fine -- clone_or_update leaves the depth-1 clone on
+        # the remote's default branch, matching PIO's lib_deps behavior
+        # and external_components handling.
         split_result = urlsplit(library.repository)
-        if not split_result.fragment.strip():
-            raise ValueError(f"Missing ref in URL {library.repository}")
 
         # Sanitize name
         name = str(split_result.path).strip("/")
@@ -377,7 +377,8 @@ def _convert_library_to_component(library: Library) -> IDFComponent:
         version = "*"
         repository = urlunsplit(split_result._replace(fragment=""))
 
-        source = GitSource(str(repository), split_result.fragment)
+        ref = split_result.fragment.strip() or None
+        source = GitSource(str(repository), ref)
 
     # Version is provided - resolve using PlatformIO registry
     elif library.version:
diff --git a/tests/unit_tests/test_espidf_component.py b/tests/unit_tests/test_espidf_component.py
index 373432f7d2..c4a419d1a2 100644
--- a/tests/unit_tests/test_espidf_component.py
+++ b/tests/unit_tests/test_espidf_component.py
@@ -436,11 +436,21 @@ def test_convert_library_with_branch_ref():
     assert result.source.ref == "some-branch"
 
 
-def test_convert_library_missing_ref():
+def test_convert_library_missing_ref_uses_default_branch():
+    """A bare URL with no #ref clones the remote's default branch.
+
+    Matches PIO's lib_deps behavior and external_components handling --
+    git.clone_or_update with ref=None leaves the depth-1 clone on
+    whatever branch the remote HEAD points at.
+    """
     lib = Library("name", None, "https://github.com/foo/bar.git")
 
-    with pytest.raises(ValueError):
-        _convert_library_to_component(lib)
+    result = _convert_library_to_component(lib)
+
+    assert result.name == "foo/bar"
+    assert result.version == "*"
+    assert isinstance(result.source, GitSource)
+    assert result.source.ref is None
 
 
 def test_convert_library_registry(monkeypatch):