Michael Ricketts has joined Middlesbrough for £3.5m plus a percentage of profits.
The former Bolton striker finalised the deal at 2330 GMT on Friday just half an hour before the close of the transfer window.
Boro boss Steve McClaren fought off competition from Premiership rivals Tottenham in the race to sign Bolton's leading scorer in the process.
A statement on Bolton's website said: "Michael Ricketts has ended his association with Bolton Wanderers by signing for Premiership rivals Middlesbrough.
"The Wanderers top scorer... put pen to paper with the Riverside club at 2330 this evening."
Ricketts, who has one England cap to date, handed in a transfer request at the Reebok Stadium over a week ago and looked set for a switch to White Hart Lane.
Spurs' offer of a part player-exchange was rejected by Bolton and Middlesbrough then became favourites to sign the player.
Boro looked to have run out of time to conclude the deal on Friday despite stating on their website at 1530 GMT that a fee had been agreed for the player.
Just hours before the close of the transfer window, Bolton insisted no official offer had been made for the player.
But Wanderers bosses finally got an acceptable bid before the transfer window closed.
Bolton, meanwhile, have made a quartet of signings to soften the blow, with strikers Salva Ballesta and Pierre-Yves Andre as well as defenders Florent Laville and Ndiwa Lord-Kangana.
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