Berbatov agreed a two-year contract with the west London team after snubbing interest from a host of clubs across Europe.
The 31-year-old had been a target for Italian sides Juventus and Fiorentina, while United manager Sir Alex Ferguson claimed on Friday that Tottenham were interested in re-signing their former star.
But Berbatov, who angered Fiorentina by deciding not to join them despite agreeing terms with the Serie A outfit, was persuaded to move to Fulham by his former Tottenham manager Martin Jol, who is now in charge at Craven Cottage.
"I'm delighted to have signed for Fulham and I look forward to playing under Martin Jol once again," Berbatov told Fulham's website.
"As soon as I was aware of Fulham's interest my decision to join was an easy one to make.
"I'm impressed with the set up here and the people have made me feel welcome. There is a close and personal feel around the club and I can't wait to get started."
Berbatov, who scored 56 goals in 149 appearances for United after a £30 million move from Tottenham in 2008, had been keen to leave Old Trafford since falling out of favour with Ferguson last season.
He finished as the Premier League's joint top-scorer in 2011, but his perceived lack of effort never made him a favourite with United fans and he was unable to convince Ferguson of his worth in the latter stages of his spell at Old Traford.
Jol hopes to revive Berbatov's career and he added: "Dimitar is a player I've always admired. He did well for me at Spurs and I'm sure that he will do well here at Fulham.
"He's a player of great quality and technical ability who will give me the attacking option I've been looking for.
"When he's not scoring goals, his ingenuity often leads to chances being created for his team-mates and I'm delighted that we've been able to convince him to come to us, as there was a lot of attention from other clubs."
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO Sports and on Facebook at AhramOnlineSports)