JOIN USButton's day in Barcelona
"I feel like I'm on top of the world at the moment," said Button, now 14 points clear of the Brazilian in the championship.
For the ninth year in a row, victory at the Circuit de Catalunya went to the driver on pole position with the Briton taking the chequered flag 13.0 seconds ahead of Barrichello for Brawn's second one-two of the season.
The Brazilian had seized the lead at the start and was dreaming of his first win since 2004 when the Mercedes-powered team switched Button from a three-stop strategy to what turned out to be a quicker two stops.
Barrichello, who stayed on three stops, looked like his world had been shattered.
"I can't believe how I lost that," the 36-year-old said, adding later that he wanted to know why the team had made the sudden decision to change the strategy while keeping him on three stops. "I'm disappointed I haven't won the race because I thought I had it in the bag today." Button commiserated and said he had not requested the change.
Australian Mark Webber was third for Red Bull, his second podium finish of the season coming on the 50th anniversary of his great compatriot Jack Brabham's first victory in Formula One, ahead of German team mate Sebastian Vettel.
Spain's Fernando Alonso had the home crowd roaring when he snatched fifth place on the final lap from Ferrari's Felipe Massa. Brazilian Massa, who led for a lap after the first pitstops, had to slow in the closing laps to save fuel with the team warning him that he risked not making it to the finish.
The three points were the first of the season for last year's overall runner-up, who had to walk back to the pits after his car crawled across the line and coasted to a halt.
Germans Nick Heidfeld in a BMW-Sauber and Nico Rosberg for Williams were seventh and eighth respectively in the first race in Europe this year.
Ferrari's 2007 champion Kimi Raikkonen, last year's winner in Barcelona, retired after less than a third of the race while McLaren's world champion Lewis Hamilton was ninth.
The safety car was deployed for four laps after a pile-up involving Toyota's Jarno Trulli, both Toro Rosso drivers and Force India's Adrian Sutil as the field powered through the second corner.
Toyota’s pull-out threat
Toyota is threatening to pull out of Formula One from 2010 because of a dispute over a proposed budget cap. Team president John Howett said unless the teams and governing body FIA could reach an agreement over next season’s cost-cuts, the Japanese team could not guarantee its future in the sport.
“From Toyota’s perspective, there are a number of concerns that really need clarifications before we commit to the future,” Howett said ahead of the Spanish Grand Prix. “We want to be here. (But) I would say it is very likely we won’t enter unless something changes significantly.”