Jenas, who has penned an 18-month deal at Loftus Road, joined Tottenham from Newcastle in 2005 for a fee of £7million and went on to make over 200 appearances for the North London club before falling out of favour.
A season long loan at Aston Villa during 2011/12 was cut short by a serious Achilles injury that kept him out for six months but despite a change of managers at White Hart Lane he could still only manage one appearance under Andre Villas Boas.
The 29-year old was sent out on loan to his first club Nottingham Forest in September and made six appearances.
He will now be hoping to revive his career with a move across London to help QPR's fight for survival and admits linking up with Redknapp was a big persuasive factor in his move to West London.
Jenas said: "Obviously the fact that Harry was here made a big difference. He knows me well as a player.
"There's a big challenge ahead and I want to be a part of it. There's no time to waste, we need to hit the ground running and get the wins, starting on Saturday."
Townsend, who also played under Redknapp at Spurs, has joined on loan until the end of the season.