Media playback is not supported on this device
The 21-year-old English swimmer was joined on the podium by Scotland's Ross Murdoch, 22, who claimed silver.
Peaty, Chris Walker-Hebborn, Siobhan-Marie O'Connor and Fran Halsall then won mixed 4x100m medley relay gold.
Halsall, 26, also took a bronze medal in women's 50m butterfly final, with 21-year-old Ben Proud finishing third in the men's event.
Media playback is not supported on this device
"There was amazing support in the venue tonight and it's definitely one of the best races I've had," said Peaty.
"And to have Ross alongside me is just great."
The reigning world and European champion set a new championship record of 58.36secs in his final and added: "That puts me in a great place going into Rio."
Great Britain's Adam Peaty won gold in the men's 100m breaststroke final at the European Championships in London.