Wimbledon runner-up Raonic will be making his second appearance at the year-ender having qualified two years ago.
He joins Novak Djokovic, Andy Murray and Stanislas Wawrinka, winners of this year's grand slam titles.
"I have had my best ever season so far this year and it is a great reward to be one of the first few players to qualify for London," the 25-year-old, who withdrew from his Beijing semi-final because of an ankle injury, said.
"I love playing indoors and I look forward to finishing 2016 hopefully on a high note."
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Four places are still up for grabs with Kei Nishikori, Gael Monfils, Dominic Thiem and Rafael Nadal currently inside the cut with two Masters Series events to come in Shanghai and Paris.
(Reporting by Martyn Herman; Editing by Toby Davis)
