Boro, who are managerless after sacking Tony Mowbray on Monday, tried to sign Ayala in the summer but a deal failed to materialise.
With the Championship club struggling with injuries in defence they have rekindled their interest and snapped him up on loan until January.
Ayala is now in line to make his debut against Doncaster Rovers on Friday evening, a game which you can see live on Sky Sports 1HD.
The former Liverpool defender joined Norwich in 2011 but injuries have hampered his stay at Carrow Road and he spent part of last season at Nottingham Forest.
Ayala will join former Norwich team-mates Jacob Butterfield and Kei Kamara at the Riverside.
Middlesbrough v Doncaster is on Sky Sports 1 on Friday night from 7.30pm