This trout is native to Europe, from the Mediterranean to the Black Sea, including Scandinavia and Siberia. It was introduced into North America in 1883 with eggs from Germany, and later by strains imported from Loch Leven in Scotland. Since then, the brown has become firmly established in many North American waters. In Canada, brown trout are abundant in southern Ontario and Quebec, as well as in southern Alberta. Extensive stocking has produced a spectacular lake-run fishery in the Great Lakes.

The brown trout has a much wider range than the brook trout, and it's been suggested they can survive in streams that will no longer support brook trout. However, brown trout don't survive well in warm, polluted water either. They can survive for a short period in 81 degree Fahrenheit water, but usually the upper lethal limit for brown trout is about 77 degrees. Brown trout prefer water ranging from 54 to 67 degrees.

The main reason for the success of brown trout in streams depleted of brook trout is probably because brown trout are harder to catch. Brown trout are competitive with brook trout in the same stream to the extent that the dominant brown trout were excluding brook trout from favorable resting (not feeding) positions in the stream, thereby making the brook trout more vulnerable to predators.