The iconic O2 Arena on the banks of the River Thames has staged the season-ending showpiece since 2009 and the original five-year deal was due to run out in 2013.
"We are very happy to announce the extension of out original commitment in London for a further two years, meaning the Barclays ATP World Tour Finals will be played in London for at least the next three years through 2015," ATP executive chairman Brad Drewett said in a statement.
"We are very proud of our marquee event, the ultimate showcase of men's tennis."
Since taking over from Shanghai as the 14th host city of the tournament that was first staged in Tokyo in 1970, London has enjoyed huge popularity with the players, the majority of whom are based in Europe, and fans.
Both day and evening sessions at the 17,000-seater venue have been near sell-outs again this year.
More than 750,000 fans attended the tournament in the first three years.
"This week we look forward to welcoming our one millionth fan through the gates at the 02 since 2009," Drewett said.
The tournament, featuring the top eight singles and doubles pairs this year, has total prize money of $5.5 million.
This year's event was brought forward two weeks in a bid to shorten the season, meaning it started on Monday, the day after the conclusion of the Paris Masters.
(Editing by Tony Jimenez)
