[2][3] Montagu's blenny is small and has an elongated body which has no scales, its eyes are set on top of the head and its mouth points downwards.

The background colour is pale brown marked with olive-green vertical stripes and light blue spots.

There is a single dorsal fin that runs along the total length of its body with an obvious notch part of the way along.

There is fringed, fleshy crest situated between its eyes and, in at least in Britain and Ireland, this feature distinguishes Montagu's blenny from the other species present.

When spawning the males become uniformly dark or show a marbled pattern and have a white upper lip.

[4] This species will stay out of the water at low tide sheltering under rocks and seaweeds,[3] being capable of breathing air.