Robin van Persie has completed his switch from Arsenal to Manchester United, signing a four-year-deal at Old Trafford.
United and Arsenal announced a fee - understood to be worth £24m - had been agreed between the clubs on Wednesday evening.
Van Persie underwent a medical yesterday and this morning signed on the dotted line of a contract which will net the Netherlands international £200,000-a-week.
Speaking about the transfer on MUTV, Ferguson revealed the 29-year-old had turned down other clubs to come to Manchester United.
"The boy wanted to come. He turned down various clubs. If he hadn't told Arsenal he wanted to go to Manchester United, the transfer wouldn't have happened," said Ferguson.
The Manchester United manager also admitted he thought it would be impossible to get Van Persie to sign, but felt compelled to make a move when the striker announced he would not sign a new contract with the north London club.
"It has given everyone a lift," said Ferguson.
"I have a complication to my life (selection). I don't know how I managed in 1999.
"They can gel together. Robin's best position is furthest up the pitch. The most important thing is to win what we want to win. These players can help us to do that."
Van Persie will be available to play in United's opening Premier League game away against Everton on Monday.
Announcing confirmation of the deal on United's website, a statement read: "Robin van Persie has completed his medical, agreed personal terms and signed for Manchester United on a four-year contract until June 2016."
The player himself said: "I am looking forward to following in the footsteps of so many great strikers, bringing my experience and playing my part to help the team compete for the biggest trophies in the game. I can't wait to get started."
United beat off competition for Van Persie's signature from Manchester City and Juventus, with the breakthrough coming when Ferguson called his Arsenal counterpart Arsene Wenger to pave the way for a deal. Originally, it appeared Arsenal would not sell the current PFA Players' Player of the Year to one of their Premier League rivals.
Arsenal remained hopeful that Van Persie may make a U-turn on his contract decision, but when he was given a hostile reception by Arsenal fans during a pre-season game in Germany, a future at the Emirates seemed impossible.
The arrival of Van Persie does not appear to be the end of Manchester United's summer transfer business either. Ferguson said today that United were seeking a new signing for "one more position" but "only if a certain player came available".