The ex-England wideman, 34, has signed a four-month deal at the Riverside and comes straight into the squad for the trip to Ipswich Town.
Dyer initially burst onto the scene at Portman Road in 1996 with his dazzling wing play, his electric pace and attacking quality eventually earning a £6.5m move to Newcastle United and international honours.
His career has been dogged by injuries since but he managed 33 caps and Middlesbrough manager Tony Mowbray reckons the capture from QPR can aid their promotion push put of the Championship.
He said: “I’ve known Kieron a long time and coached him for a year or two at Ipswich before he moved on.
“At such a young age he was a fabulous footballer and he’s still a fabulous footballer.
“Obviously he’s had injury problems for a lot of years. People keep throwing statistics at me of how many games he’s played and for how long, but I look at his record of where he has played this year.
“I watched him play against Manchester United this season and against Gareth Bale at Tottenham and he was fine.
“We’ll have to see how he handles the intensity required in this league.”
Mowbray continued: “It’s a deal that suits both parties. Kieron and his advisors have been very, very honourable in the discussions.
“He’s a good lad and a good pro. He wants to play football and he’s happy to be here – hopefully he can contribute and help us succeed.”
Dyer last played in QPR’s FA Cup game against West Bromwich Albion four weeks ago scoring in the 1-1 draw before being released by Harry Redknapp in the transfer window.
The ex-West Ham player was sometimes used at right-back by Rangers but Mowbray admits it is his obvious creativity which he hopes to see in Boro colours.
“I’d have to say he’s not been brought here to play right-back,” he said. “He can play anywhere across the midfield – left, right, centre, in a three-man midfield or two-man midfield – because he understands football.”