And Croatian international midfielder Niko Kranjcar will also come to Loftus Road on a similar deal.
Cameroon international full-back Assou-Ekotto and England U21 international midfielder Carroll will be linking up once again with QPR boss Harry Redknapp, having previously worked with him when he was in charge at Spurs.
QPR were relegated from the Premier League last season but lie second in the Championship after a good start to life back in the second tier and Redknapp is delighted with their newest acquisitions.
"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," said the manager.
"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.
"And 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 for 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."
Assou-Ekotto said: "It is fantastic to be linking up with Harry again. I enjoyed my best form at Spurs under him and am looking forward to doing my best for QPR.
"I know the way Harry likes his sides to play, and it is a style that suits me, which is why I am excited about this opportunity. QPR have made a great start and I can't wait to help them build on that during my time here."
Carroll is also excited about linking up with Redknapp again and said: "I am delighted to come here and really excited. Harry was a big factor for me, because of how he likes the game to be played.
"The important thing for me now at this time in my career is to be playing regular football and hopefully I can achieve that here. I've seen what (his Tottenham team-mates) Kyle (Walker) and Andros (Townsend) got from their loans at Loftus Road, and I hope I can enjoy similar success."
The 29-year-old Kranjcar joins on loan from Dynamo Kiev, having previously been signed by Redknapp for Portsmouth and Tottenham.
"Niko's a crowd pleaser, he gets people off their seats," said Redknapp. "He's a top player and someone who will add great quality to the squad.
"He can play in a variety of positions, off the front-man, out wide on either side, and he's always a threat. He gets at players and makes things happen.
"He's someone I obviously know a lot about and he'll be a fantastic addition for us."
Kranjcar said: "Harry has always brought the best out of me as a player. I played for him in two separate spells in England, and I am delighted to be linking up with him again, this time at QPR.
"The Championship is a new experience for me but it is a challenge I'm excited about. I just want to play games and help QPR get promotion back to the Premier League."