Ighalo sealed a Deadline Day loan move to United from Chinese Super League side Shanghai Shenhua.
Speaking after arriving, Ighalo wearing a hoodie, he said he is relishing the chance to prove himself at Old Trafford.
“It’s a dream come true because since I was a kid I followed and dreamt of Manchester United,” Ighalo told Sky Sports News.
“But it is a reality now. I cannot say much more now until I get started.”
Reflecting on a hectic last few days before the transfer went through, Ighalo said: “It’s been crazy. Obviously, I am happy to be in Manchester first of all.
“This is a great opportunity for me and I am grateful to God, and to my agent, and the coach who has given me this opportunity to be here.
“I am happy to be here and to work out with the team and finish very well this season.
“The plan is to just chill today because I travelled a very long way from Shanghai to Manchester.
“Today is to just rest and tomorrow we start to work.”
United boss Ole Gunnar Solskjaer is confident Ighalo will thrive at the club, having scored 16 goals in 55 Premier League games during his time at Watford.
“Odion is an experienced player,” Solskjaer said.
“He will come in and give us an option of a different type of centre-forward for the short spell he’s staying with us.
“A great lad and very professional, he will make the most of his time here.”