The unseeded Americans defeated fifth seeds Timea Babos of Hungary and Yaroslava Shvedova of Kazakhstan 6-3, 6-4 to claim their sixth Wimbledon doubles title.
It was also their 14th doubles triumph as a team at the majors and their 22nd in 23 finals overall.
The sisters last lost a doubles final in 1999 in San Diego.
"It's awesome to win another doubles at Wimbledon," said Serena.
Venus said: "I never want to make a mistake. I don't want to let Serena down. She brought the energy from the singles on to the doubles court."
Earlier yesterday, Serena had defeated Angelique Kerber 7-5, 6-3 in the women's singles final.
