Striker Lukaku admitted watching his new teammates during the Europa League final helped make up his mind on his future.
Jose Mourinho’s men picked up their third piece of silverware of last season with a 2-0 win over Ajax to lift the Europa League – and qualify for the Champions League.
Goal machine Lukaku confirmed his switch from Everton to United for £75m on Monday afernoon.
“I would like to start by thanking Everton and the fans for the last four wonderful seasons, I have made some special friends and we have shared some amazing moments,” Lukaku who signed a five-year contract at Old Trafford.
“However, when Manchester United and Jose Mourinho come knocking at the door it is an opportunity of a lifetime and one that I could not turn down.
“You could see the fight, determination and the spirit in this team during the Europa League final and I want to become a part of that.
“I cannot wait to run out at Old Trafford in front of 75,000 fans but before that pre-season is where the hard work starts and I am looking forward to that first training session.”
Boss Mourinho, who allowed the Belgian hit man to leave Chelsea for the Toffees in 2014, is looking forward to working with him again.
“Romelu is a natural fit for Manchester United,” the Portuguese said. “He is a big personality and a big player. It is only natural that he wants to develop his career at the biggest club.
He will be a great addition to the group and I know they will make him very welcome. I am really looking forward to working with him again.”