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Federer will top Group B after producing his third dominant display at this year's prestigious end-of-season event at London's O2 Arena.
The world number two's victory also means Andy Murray can book his spot in the last four by beating David Ferrer later on Thursday.
Soderling's only hope of qualifying is if Ferrer defeats Murray in two sets, a result which would bring into play the tournament's complex rules involving the percentage of games won by each player.
The Tour Finals' round-robin system forces every player to reach for the calculator to work out the various permutations that could see them through.
For Federer at least, the equation was relatively simple. The 29-year-old just needed to win one set to be guaranteed top spot in the group, while Soderling's potential path to the last four was rather more headache-inducing.
After a disappointing season, which saw him lose the French Open and Wimbledon titles he won in 2009 as well as the number one ranking, Federer has been in rare form over the last few days at the O2 Arena.
His imperious display against Murray on Tuesday followed an equally convincing straight sets win over Ferrer and a record of 14 wins from 15 previous meetings with Soderling suggested he would get what he needed to qualify.
It took the six-time Wimbledon champion just three games to secure the first break as Soderling self-destructed with three successive unforced errors.
Yet when the Swede found his range with his booming groundstrokes he managed to push Federer to the baseline.
Soderling's baseline barrage kept Federer off balance in the eighth game and forced the Swiss into some uncharacteristic errors which allowed the world number four to break back.
Soderling's one success against the world number two came in the French Open quarter-finals this year and he was starting to rattle Federer in much the same way he had on the clay at Roland Garros.
But Federer is a different animal on hard courts and he regained his composure quickly enough to ensure the set went to a tie-break.
A sublime forehand from Federer secured two set-points in the breaker and he converted the second with a blocked backhand that Soderling opted to leave, only to turn and watch in horror as it clipped the line.
That misjudgement was enough to book Federer's semi-final place but Soderling was still fighting for his tournament life and he missed a chance to get back in the match when he squandered two break points at the start of the second set.
Although Soderling fought off two break points in a marathon fourth game, Federer secured the only break of the second set with a tremendous whipped forehand winner before serving out the match.
