The breeding plumage is mainly brown, with pale feather edges giving a scaly appearance; the central underparts, normally below the surface on a swimming bird, are white.

In breeding plumage it shows a pale throat which is absent in marbled murrelet, and weaker scaling because of fewer rusty and buff markings.

Measurements:[5] The long-billed murrelet feeds at sea principally on small fish, both in pelagic offshore areas (often associating with upwellings), and inshore in protected bays.

Unlike most other seabirds, it does not breed in colonies or even necessarily close to the sea, instead nesting in on branches of old-growth conifers.

The species is unusually prone to vagrancy, with records in both North America and Europe, often at inland sites well away from its usual ocean habitat.

There are about 40 records from North America (Mlodinow 1997), half of them on the Pacific coast where they might be expected, but the rest scattered across the continent east to Florida, Pennsylvania, New Jersey, New York, Massachusetts, North Carolina, South Carolina and Newfoundland, as well as on lakes and rivers several hundred kilometers from the sea, in Colorado (two), Indiana (three), Montana, Ohio, Kentucky, Tennessee, Arkansas, Wyoming (two), and Kansas (two).

The first found in Europe was a first-winter individual discovered drowned in a fishing net at Zollikon, Lake Zurich, Switzerland on a date between 15 and 18 December 1997.