The 34-year-old American and top seed matched Steffi Graf's Open Era for majors -- on her fourth try -- with the victory in the Wimbledon final on Centre Court at the All England Club in London. Margaret Court holds the all-time record with 24 Grand Slam titles. The Open Era began in 1968.
After the win, Williams raised two fingers on each hand to show off the magic number.
"Yeah, it's been incredibly difficult not to think about it. I had a couple of tries this year," Williams said during the trophy ceremony on matching Graf's record. "But it makes the victory even sweeter to know how hard I worked for it.
"I have, yeah, definitely had some sleepless nights, if I'm just honest, with a lot of stuff. Coming so close. Feeling it, not quite able to get there."
Venus Williams, Serena's older sister and doubles partner, was watching in her guest box.
"This court definitely feels like home, I have a match later today in the doubles (final on Centre Court), so I'll be back out," Serena Williams told the BBC. "I don't know what else to say, I'm so excited."
Williams hit 13 aces and won 38 of 43 points when the world No. 1 put a first serve in.
"Angelique, I love playing her, she brings out great tennis in me and off court she's a wonderful person to be around," Williams said.
Williams became the fourth woman in the Open Era to win seven or more singles titles at a Grand Slam event. Martina Navratilova won nine titles at Wimbledon, Graf won seven at Wimbledon and Chris Evert won seven at the French Open.
Williams won her first major title since Wimbledon last year. Since then, she lost in the U.S. Open semifinals and in the final of the Australian and French Opens.
Kerber, the No. 4 seed from Germany, beat Williams in the Australian Open final for her first Grand Slam title.
"First of all I would like to say congrats to Serena," Kerber told the BBC. "You really deserve it, you are a great champion, a great person and it is always an honor to play against her.
"It is the best feeling to play here on Centre Court, you guys are amazing. It is an honor to play here on this court and I would like to say thank you to my box you are amazing, I have the best team and sometimes I am not so easy but you always believe in me."
Serena and Venus Williams later won their sixth doubles championship at the All England Club and 14th as a pair at all Grand Slam tournaments. They beat fifth-seeded Timea Babos of Hungary and Yaroslava Shvedova of Russia 6-3, 6-4.
The Williams sisters also won the doubles title at Wimbledon in 2000, 2002, 2008, 2009 and 2012. Each time, one of them also won the singles title and headed home with two trophies. They are now 14-0 in major doubles finals.
On Sunday in the men's final, second-seeded Andy Murray of Great Britain, the 2013 champion, takes on No. 6 Milos Raonic, a Canadian making his debut in a Grand Slam final.