Kerber will become just the 12th woman to finish the year ranked number one since 1975
Regardless of how she performs in Singapore, Kerber will be presented with the year-end number one trophy after Williams, the only woman with any chance of overtaking her at the top of the rankings, pulled out of the elite eight-player tournament with a shoulder injury.
Kerber will become just the 12th woman to finish the year ranked number one since computer rankings were introduced in 1975, and no one would begrudge the 28-year-old's claim to the title after a career-best season in which she lifted the Australian and US Open trophies and finished runner-up at Wimbledon and the Rio Olympics.
"This is one of the things I have been dreaming of," Kerber said. "I have worked extremely hard to become the best player I can be and this is a reflection of that effort and the wonderful year I have had."
With the ranking trophy safely in the bag, Kerber now has her sights on picking up another major piece of silverware, the Billie Jean King Trophy for the winner of the prestigious end-of-season tournament.
Restricted to the world's top eight players, the WTA Finals is regarded as the most important annual event in women's tennis outside the four majors, boasting a star-studded honour roll.
While Williams has won the tournament five times, Kerber has only qualified twice before, in 2012 and 2013, bowing out in the round-robin phase each time, giving her added incentive to cap her year by winning the October 30 final.
She will go into the event as the favourite this time but facing a tough challenge from a strong and deceptively deep field, which includes last year's winner, Poland's Agnieszka Radwanska, and reigning French Open champion Garbine Muguruza of Spain.
Muguruza had her own breakout year in 2015, reaching the Wimbledon final then the semis in her first appearance at the WTA Finals.
This year, the 23-year-old went one better, claiming her first major when she upset Williams in the French Open final. She now wants to make another statement on the indoor court of Singapore.
"I think the important tournaments are the ones you've got to play well, the ones that really count, the ones that really take you to the top level," she said.
"I just have a very aggressive game. I go for my shots with no regrets, even if I have to play to the fence."
Romania's Simona Halep, runner-up two years ago, has also qualified for Singapore, along with Czech Karolina Pliskova, who ended Williams' reign as world number one in the semi-finals of the US Open, as well as American Madison Keys and Dominika Cilbulkova of Slovakia.
Even though the tournament starts on Sunday, the last qualifying spot remains undecided with Britain's Johanna Konta tentatively booked to compete but at risk of being overtaken in the rankings by Svetlana Kuznetsova, if the Russian wins this weekend's Kremlin Cup in Moscow.
"If I win the tournament, it would be amazing and that's what I'm expecting," Kuznetsova said.