The northern beardless tyrannulet is  long, and weighs . The head is dark brown with an erectile crest and pale supercilium. The upperparts are grey-green becoming paler on the rump.
In terms of physical characteristics, the northern beardless tyrannulet is notable for its considerable length and substantial weight. The distinctive dark brown coloration on its head, accompanied by an erect crest and pale facial markings, sets it apart. Additionally, its upper body exhibits a unique grey-green plumage that transitions to a paler tone towards the rear end.