Ranging from the lower Great Lakes region to northern Mexico, it has been widely introduced and is an invasive species in some areas.

The closest living relative of the flathead catfish is the much smaller widemouth blindcat, Satan eurystomus, a cavefish.

Individuals, particularly young specimens from clearer waters,[6] may be strongly mottled with dark brown to black color.

[6] The world angling record flathead catfish was caught May 19, 1998, from Elk City Reservoir, Kansas, and weighed 55.79 kg (123.0 lb).

[11] The native range of the flathead catfish includes a broad area west of the Appalachian Mountains encompassing large rivers of the Mississippi, Missouri, and Ohio basins.

These catfish prefer medium to large sized rivers with relatively warm water and stable slow moving currents.

Flathead catfish tend to have a home range of less than 2 kilometres (1.2 mi), this means that they are a non-migratory species of fish.

[5] They are known to eat crayfish, American gizzard shad (Dorosoma cepedianum), insects and larvae, channel catfish (Ictalurus punctatus), drum (Aplodinotus grunniens), other flatheads, green sunfish (Lepomis cyanellus), and carp.

Insect larvae are the major prey type until an individual reaches approximately 100 mm (3.9 in) in total length, at which point the diet expands to include crayfish and small fishes.

[17] Spawning of P. olivaris occurs in late June and early July, and the nests are made in areas with submerged logs and other debris.

[13] The fry frequent shallow areas with rocky and sandy substrates, where they feed on insects and worms such as annelids and polychaetes.