The England midfielder agreed a three-year deal with the Craven Cottage club and moved across London to join Martin Jol's Cottagers for an undisclosed fee.
Parker, 32, moved to White Hart Lane from West Ham in August, 2011.
He made 34 appearances in a successful first season but was blighted by injury last term.
Parker returned to first team action in December and went on to make 29 appearances in all competitions but was surplus to Andre Villas-Boas's midfield plans this campaign.
Parker said: "I'm delighted to be joining Fulham and I'm looking forward to meeting my new team-mates at training tomorrow morning.
"Fulham is an established Premier League club and I look forward to trying to help the team progress even further over the next three years."
Parker started his career at Charlton, before moving to Chelsea. He then then headed to Newcastle, but returned 'home' for a successful spell with West Ham during which he was named as the Football Writers' Association Player of the Year.
United's relegation from the Premier League paved the way for Parker to move to Spurs, and it was while at White Hart Lane that he was asked to captain England in a friendly against Holland.
He started every group match at Euro 2012 and has made 18 England appearances, adding to in excess of 300 Premier League matches.
"I'm delighted that Scott has joined us," manager Martin Jol said.
"He's a midfielder who works tirelessly for his team and is a fantastic player both on and off the ball.
"It is wonderful to see a player of his stature playing for Fulham Football Club as he has shown his qualities in the Premier League and for the England team for many years.
"I'm happy that he's here and joins us for training ahead of our first home match of the season."
QPR confirmed last Friday that a deal had been agreed with Spurs and manager Harry Redknapp was hoping Parker would accept a move to Loftus Road.
Redknapp said: "It's down to Scott now. The chairman has agreed a deal with Tottenham. It's up to Scotty now.
"Hopefully Scotty will feel the same and come here. We feel this is a club progressing and we'd love him to be part of it here."
The Championship club also lost out to a Premier League team for Gary Hooper earlier this summer after the striker opted to join Norwich City from Celtic.