Media playback is not supported on this device
Adams, 32, beat Poland's Sandra Drabik on a majority points decision to win Britain's 13th gold in Azerbaijan.
Duncan Scott added a 14th with victory in the men's 100m freestyle, lifting Britain up to third in the medal table.
The 18-year-old won in 49.43 seconds, with Italy's Alessandro Miressi second and Russia's Vladislav Kozlov third.
Scott returned for the men's 4x200m final where he, Martyn Walton, Kyle Chisholm and Cameron Kurle finished second to Russia, with bronze going to Germany.
Jarvis Parkinson won silver in the men's 200m individual medley, with Walton in third, while Layla Black also claimed bronze in the women's 200m breaststroke final.
Black then joined Rebecca Sherwin, Amelia Clynes and Georgia Coates to win bronze in the women's 4x100m medley relay behind Russia and the Netherlands.
"I'm bringing back a little piece of history for Great Britain," said Adams, whose fellow British boxer Joe Joyce will compete in the men's super-heavyweight final on Friday.
The 29-year-old from London won his semi-final against Tony Yoko of France by unanimous decision and will fight Russia's Gasan Gimbatov. The win means Joyce has secured a place at the World Championships in October, where he will have the chance to qualify for the Rio Olympics.
Meanwhile, Sandy Ryan took bronze at women's light-welterweight after losing her semi-final to Russia's Anastasia Beliakova.
The European Games conclude on Sunday, 28 June.
Olympic boxing champion Nicola Adams won flyweight gold on a day when Great Britain claimed a further six swimming medals at the European Games in Baku.