The former Sunderland and Stoke midfielder has been in talks with Boro for a number of weeks, following his release from the Britannia Stadium.
Whitehead has now penned a two-year deal with Boro to become their second signing of the summer following on from the capture of Jozsef Varga.
The 31-year-old makes a return to the North East having spent five years with Sunderland, prior to his move to Stoke.
"This is a fresh start for me and I'm looking forward to it," he told Boro+.
"I had five or six options, but having spoken to the manager (Tony Mowbray) early in the summer I had a good feel for him and this place.
"I know the way he likes to play and I know there are a lot of good players here.
"There is a lot of talent here and I think the manager and chairman have this cub heading the right way again. I hope I can help them achieve what they deserve."