After hitting a backhand winner on match point, she fell onto her back to the grass. She then rose with a grin as big sister Venus - another five-time Wimbledon champion - smiled and applauded, along with the rest of the crowd.
After shaking hands with Radwanska, Williams climbed into the box where her family was seated. She hugged her father, Venus, their mother and others.
Out on court, Williams had little trouble at the start, using her hard serve and powerful groundstrokes to win the first five games and run Radwanska all over the grass.
Radwanska, who was playing in her first Grand Slam final, has been ill with a respiratory problem, making it difficult for her to speak. In the second set and already down a break, the third-seeded Pole was coughing and blowing her nose during a changeover.
But she broke Williams in the next game to even the score at 4-4, and then broke again to win the second set.
Williams responded in the third set, breaking twice and serving out to win another major title.
The match was played with the Centre Court roof open, and it was delayed by rain for a short time after the first set.
Later Saturday, Serena and Venus Williams will play in the doubles final.
A little more than a month ago, many started writing Williams off for good. She lost in the first round of this year's French Open, the first time she had ever exited a Grand Slam tournament that early.
But at Wimbledon, she looked every bit a champion again.
She broke her own tournament record for aces in a match with 23 against Zheng Jie in the third round. Less than a week later, she eclipsed that mark with 24 against Victoria Azarenka in the semifinals.
On Saturday, she finished with 17 aces and a record 102 for the tournament.
It was Williams' first Grand Slam title since she won at the All England Club two years ago. But she has had to overcome some off-the-court health issues to get back to the top. Shortly after winning at Wimbledon in 2010, Williams cut her feet on glass at a restaurant, leading to a series of health problems, including being hospitalized for clots in her lungs.
Williams is the first woman in her 30s to win a Wimbledon title since Martina Navratilova, who won at the All England Club in 1990 when she was 33.
In the men's final on Sunday, six-time Wimbledon champion Roger Federer will face British hope Andy Murray. The fourth-seeded Murray is trying to become the first British man to win the title at the All England Club since Fred Perry in 1936.