Watson and Kontinen beat Cololmbian Robert Farah and Anna-Lena Gronefeld of Germany 7-6 (7-5) 6-4 to win the mixed doubles title - a victory which made Watson the first British woman since 1987 to win a title of any sort at SW19. Kontinen also made history, becoming Finland's first-ever grand slam champion.
The victory completed an incredible day for home-grown players, with four finalists all winning.
First up came Scotland's Gordon Reid, who won the inaugural Wimbledon men's wheelchair tennis singles title, beating Sweden's Stefan Olsson in the final.
The 24-year-old Reid, who had already won the doubles title with Alfie Hewitt, beat Olsson 6-1 6-4 to claim the first ever men's singles wheelchair title at the All England Club.
Nerves looked to affect him when Reid double-faulted on his first match point, but on the second Olsson sliced a backhand into the net and the home crowd roared its delight, chanting "Reid-o, Reid-o".
Shortly afterwards Jordanne Whiley won the women's wheelchair doubles final alongside Japan's Yu Kamiji, beating Jiske Griffioen and Aniek van Koot of the Netherlands 6-2 6-2.
Then it was the turn of Andy Murray, who beat Milos Raonic in straight sets in a one-sided men's singles final.
That left the stage open for Watson to add to the British glory as she won the mixed doubles final alongside Finland's Kontinen, and complete perhaps the greatest day ever for British players at Wimbledon.
Additional reporting by PA
Read the original article on Eurosport: Heather Watson wins mixed doubles to complete miracle day for Brits at Wimbledon