The Dutch superstar will wear the No 20 shirt after completing his £24million switch from Arsenal.
He has signed a four-year contract worth an incredible £250,000 per week - the same terms handed to Wayne Rooney two years ago.
Speaking at his official unveiling press conference, he said: 'In these situations, when you have to make a hard decision in your life, I always listen to that little boy inside me. What does he want? That boy was screaming for Manchester United.
'Manchester United breathes football. If you look at all the players from Manchester United, the stadium and manager, my choice was made very soon.'
His new strike partner Rooney posted on Twitter: '@Persie_Official welcome to manchester united mate.'
Van Persie, who could now make his debut at Everton on Monday night, arrived at Manchester United's training ground on Friday morning to sign his new £12million-a-year contract.
The Dutch international underwent a medical in Manchester on Thursday night before spending the night in a Cheshire hotel.
Van Persie then trained with his new club and is expected to go straight in to the team for the season's opener at Everton on Monday.
Sir Alex Ferguson said: 'Robin is a world-class striker with a proven record in England and in European football.
'His talents need no introduction to our fans – he has scored a number of goals against us in some classic battles with his former club. His movement, finishing and all-round ability are outstanding.
He later told MUTV: '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.'
Ferguson admitted he thought it would be impossible to get Van Persie to sign, but had to make an attempt when the striker did not sign a new contract with the north London club.
At the press conference, Ferguson added: 'We never thought we could get Van Persie. If you go back six months ago, I couldn't see us getting him.
I thought Arsenal are not going to let him go. When I read he had refused a new contract, that is when we acted. It has been a long haul.'
Even so, it took a personal intervention from Ferguson to get the deal moving last week after it had apparently stalled permanently.
'I can't elaborate but it was amicable,' said the Scot. 'Arsene knew the boy wanted to leave. He knew he wanted to join us. That made it a bit easier but not in terms of trying to reduce the fee.
'He (Wenger) could run a poker school in Govan. He got a great price but we are also happy the matter is concluded. From the starting position when we first started negotiating, Arsene has done well.'
Ferguson revealed he was still looking at a new signing for 'one more position' but 'only if a certain player came available'.
Van Persie's old Arsenal team-mate Cesc Fabregas tweeted: 'As a friend and team mate of mine for the last 8 years i want to wish good luck to @Persie_Official and his new adventure at Man United.'
United are understood to have agreed a £15m downpayment for last season’s Footballer of the Year and Players’ Player — who scored 30 Premier League goals for last season. That will rise to £24m depending on appearances. Van Persie is expected to sign a four-year contract worth over £200,000 a week.
In signing Van Persie, United manager Sir Alex Ferguson has laid down a clear marker ahead of the new season. It is the first time the club have paid for a big name since Dimitar Berbatov from Tottenham for £30.75m in 2008.