Button races to 1st pole for McLaren in Belgium
Button, who has never qualified higher than fifth at the Spa-Francorchamps circuit, put in a surging penultimate lap that would have been enough for pole regardless of his final run, which was faster still.
"Woohoo!" said a jubilant Button on the team radio.
Japan's Kamui Kobiyashi came a surprise second in his Sauber to join the Briton on the front of the grid 0.3 seconds back, with Pastor Maldonado finishing 0.32 adrift for third place in the Williams.
Sergio Perez in the other Sauber will start in fifth, with championship leader Ferrari's Fernando Alonso, who topped the practice times, in sixth.
Mark Webber achieved the seventh-fastest time but has a five-place grid penalty for an illegal gearbox change and must start in 12th, promoting Lewis Hamilton to seventh.
World champion Sebastian Vettel, last year's pole sitter, failed to make the final qualification session in a miserable afternoon for Red Bull, along with Michael Schumacher, and starts 11th, with the seven-time title winner 13th.
"Sorry guys, I had no more in it," Schumacher said on the team radio.
The Caterham pair of Heikki Kovalainen and Russia's Vitaly Petrov could manage only 19th and 20th, respectively.