Owen, who finalised his move on Friday after a day of talks with Sir Alex Ferguson at United's Carrington training ground, admitted he agreed to the move 'without a moment's thought'.
The striker will take take a substantial cut to his £110,000-a-week wages at Newcastle, although he will earn a similar figure if clauses related to goals, appearances and success are met.
He said: 'I had just begun to talk to other clubs when out of the blue Sir Alex phoned me on Wednesday afternoon and invited me to have breakfast with him the next morning, during which he told me he wanted to sign me. I agreed without a moment's thought.
'This is a fantastic opportunity for me and I intend to seize it with both hands. I am looking forward to being a Manchester United player. I want to thank Sir Alex for the faith he has shown in me and I give him my assurance I will repay him with goals and performances.'
The former Liverpool player passed one test on his troublesome knee in London on Thursday before undergoing further tests at Carrington yesterday morning. After being shown round United's state-of-the-art facilities, the striker travelled to Bridgewater Hospital, in Manchester city centre, for a full medical examination. The formalities of the deal, which is believed to be worth a basic salary of around £30,000-a-week, were concluded on Friday evening.
Owen is expected to be officially presented as a United player when the club's first team squad return to training next week.
Ferguson said: 'Michael is a world-class forward with a proven goalscoring record at the highest level and that has never been in question. Coming here with the expectations we have is something Michael will relish.'
Owen's contract with Newcastle expired on Wednesday and his advisers, Wasserman Media Group, reportedly concerned by the number of acceptable suitors, had even taken the unusual step of sending a brochure detailing his talents and medical records to a number of Premier League clubs.
Hull, Tottenham and Aston Villa were all believed to be considering offers, while Everton last week presented him with a deal worth around £50,000-a-week. It is thought clubs in Italy and Spain had also registered an interest despite both Blackburn and Wigan both expressing doubts over his ability to recapture the form which once made him European Footballer of the Year.
Ferguson denied in May he would consider a move for Owen and sources close to the club had intimated the Scot was prepared to finish his summer spending after the capture of Luis Antonio Valencia from Wigan for £16 million on Monday.
It is thought Ferguson's failure to land Karim Benzema, David Villa and Franck Ribery as replacements for Carlos Tevez and Cristiano Ronaldo, though, forced a rethink and tempted him to move for a player he missed out on as a junior and spurned the chance to sign when he left Real Madrid in 2005.