The top seeded Spaniard, hoping to emulate the great Bjorn Borg as a six-time Paris champion, will tackle British fourth seed Andy Murray for a place in the final.
It was Nadal’s second successive French Open win over fifth seed Söderling after his victory in the 2010 final had avenged his stunning fourth round defeat to the Swede the year before, still Nadal’s only loss in Paris against 43 wins.
Despite being on the verge of losing his world number one spot to Novak Djokovic, who he could yet meet in Sunday’s title match, Nadal shook off the shackles which had restricted his performances in the earlier rounds.
Söderling, for his part, was undone by 41 unforced errors.
“I played a very tough opponent. I’m happy I’m through to the semis,” said Nadal.
“I was much better than in previous matches. I was more solid and Robin made more mistakes than usual.”
Nadal was 3-0 up with a double break in the first set, the second of which was created by a sweet backhand pass, picked off his toes.
Söderling, the runner-up in 2009 and 2010, clawed back one of the breaks but Nadal, mixing breathtaking defence and accuracy from the back of court, got the best of a series of gruelling, rallies to take the 49-minute opener.
The energy sapped from the big, 26-year-old Swede in the second set.
He was broken three times while Nadal, comfortably playing his best tennis of the tournament, allowed him just three points on his own service while committing only two unforced errors.
Nothing illustrated Nadal’s renewed sense of purpose more than at 30-30 in the first game of the third set.
Twice he had to stretch to hit defensive backhands from behind the baseline before sprinting to prod back a Söderling drop shot. Despite being off-balance, the 24-year-old still managed to execute a winning smash.
Söderling was broken to trail 0-2 in the next game before he took advantage of a sloppy Nadal service game to retrieve the break.
That spured him into a new lease of life and Nadal was forced to fight off three break points in a tense 11th game, secured by a wrong-footing forehand after another punishing rally.
Söderling was 0-30 down in the 12th game but his big serve got him out of trouble as the tie break loomed.
But Nadal went to three match points in the breaker, courtesy of a sweeping forehand down-the-line winner, and took victory when Söderling netted a forehand.
In Friday’s other semi-final second seed Djokovic, on a 43-match winning streak, faces 2009 champion and second seed Roger Federer.