The 30-year-old Nigeria forward has joined United on loan from Shanghai Shenhua until the end of the season.
The ex-Watford player says his mum cried at the news and there were parties on the street where he grew up.
“A few other clubs had shown interest, I said: ‘Please, just pick United, if it’s going to be possible,'” he said.
Speaking to the club website, he added: “At 11pm in Shanghai, my agent called me [to say] that United want to do the deal, so I woke up that night and started looking for a translator to go to the directors’ room and hit his door.
“‘My agent wants to speak to you. United are coming for me, you have to make this happen.'”
Ighalo, his agent and the clubs spent the night negotiating and signing paperwork to get it through before the deadline at 7am Shanghai time.
Meanwhile, other clubs were calling asking Ighalo to sign for them.
“I told my agent ‘this is what I want. I want to come here’,” added Ighalo.
“He said: ‘You’re going to get a pay cut to go to United.’
“I said: ‘I don’t care. Make this deal happen. I want to go to United. I don’t care how much is the pay cut, I know that, make it happen.'”
Ighalo says he has been a United fan since he was a child and is pleased to be able to make the his dream of playing for the Old Trafford club a reality.
“I called my mum and she was happy, crying,” he said.
“I know many people used to say when they join a team, they say that they dream of playing for that team. Mine was not the case. I supported the team when I was young.
“People that know me, even back in Nigeria, and even when I was playing at Watford, my team-mates knew that I loved Manchester United, I support them.”
With Marcus Rashford recovering from a stress fracture and Anthony Martial having scored once in his past five Premier League games, Ighalo hopes his physicality can aid the United forward line.
“I’m very fast, I’m skilful, I’m strong, I have good techniques, so I can find my way in the field of play,” he said.
“They have a striker that stays mostly in the middle, but Martial likes to come from the side, even Rashford, so you need someone in the middle that can keep the ball, hold the ball.
“They need a physicality up front to keep the ball, to give and to make some movement, which I believe if everything goes well I can add to the team.”