The American started the year poorly amid concerns over her fitness and motivation and lost in the fourth round of the Australian Open.
But back-to-back tournament wins in Charleston and Madrid in April and May marked a remarkable change in fortune for her.
Williams, who turned 31 in September, went on to win 48 of 50 matches, landing Grand Slam titles at Wimbledon and the US Open and taking gold in London where she defeated Maria Sharapova 6-0, 6-1 in the final.
She then finished the year in fitting style by winning the WTA Tour Championships in Istanbul although she remained ranked third in the world behind Victoria Azarenka and Sharapova.
After her win in Turkey she said: “I’ve always said if I’m playing well and doing everything right, it’s really difficult to beat me.
“I still believe that, which is great that I can still kind of play that way. I feel like there are always ways for me to improve, but I think it’s a true statement, without trying to sound really full of myself or anything.”
Williams was previously honoured with the WTA award in in 2002, 2008 and 2009.
In the 36-year history of the Player Of The Year award, Williams is one of only three players to win it more than twice, alongside eight-time winner Steffi Graf and seven-time winner Martina Navratilova.
Four players have won the award twice – Monica Seles, Lindsay Davenport, Justine Henin and Kim Clijsters.