Assou-Ekotto, 29, had been a regular at Spurs for four seasons, but has recently lost his place at left-back to Danny Rose, and will now link up with former Lillywhites boss Harry Redknapp at Loftus Road.
Redknapp told QPR's official website: "Benoit, for me, is one of the best left backs in the Premier League, so I'm delighted we've been able to bring him here.
"I really think he's top class. He played for me every week at Tottenham and never let me down once. He's a great lad and will add great quality to the squad."
England Under-21 international Carroll is a highly-rated midfield prospect at White Hart Lane, but manager Andre Villas-Boas was willing to let him leave temporarily in order to gain first-team experience.
On Carroll, Redknapp added: "Tom's a fantastic signing for us on loan. He's a player I fully expect to go to the very top of the game – he's a future England international.
"I played him at Spurs in Europe and he was fantastic for me. He's got all the attributes to be a top, top player. He can pass, he can create, he can score goals – he's a fantastic player and I'm confident he'll flourish here for us."
Redknapp also revealed that Rangers are working on a deal to bring another former Spurs player, Niko Kranjcar, to West London.