The 65-year-old Englishman took Spurs from the bottom of the Premier League to the Champions League before being fired by the north London club in June despite finishing fourth.
Now Redknapp is taking control of another winless London club that is at the bottom of the standings, with QPR amassing just four points from 12 games before Mark Hughes was fired on Friday.
After signing a 2 1/2-year contract on Saturday, Redknapp said QPR hasn't been performing to its potential.
"There's no doubt there's a lot of ability in the squad, but for one reason or another things haven't gone as well as everyone expected since the start of the season," he said. "I can't wait to get to work and get the results necessary to kick-start our season."
Redknapp will be in the stands at Manchester United on Saturday as assistant coaches Mark Bowen and Eddie Niedzwiecki take charge of QPR, which only survived in the Premier League on the last day of last season.
"The players have got to step up and start performing," Redknapp said.
And there's no one better than Redknapp to achieve that, according to chairman Tony Fernandes.
"He has a proven track record in the Premier League and has all the characteristics we were looking for to get us out of the current situation we find ourselves in," Fernandes said. "His man-management skills are second to none and we are confident he is the right man to lead us away from the bottom of the table."
Fernandes signed 11 new players in the summer transfer window, including Park Ji-sung from Manchester United, Jose Bosingwa from Chelsea and Julio Cesar from Inter Milan, but they have failed to jell.
"We believe we have a manager with significant experience at the highest level of football, who can come in and immediately help deliver our objectives," Fernandes said.