Ibrahimovic joins The Red Devils on a free transfer from French Ligue 1 outfit Paris Saint-Germain, where he managed 156 goals in 180 appearances.
The 34-year-old, who has won championships in four different leagues, says he is relishing his Premier League debut as well as working with his former Inter Milan boss.
"I am absolutely delighted to be joining Manchester United and am looking forward to playing in the Premier League," Ibrahimovic told United's official website.
"It goes without saying that I cannot wait to work with Jose Mourinho once again. He is a fantastic manager and I am ready for this new and exciting challenge.
"I have thoroughly enjoyed my career so far and have some great memories. I am now ready to create more special memories in England."
Meanwhile, the Portuguese tactician believes his new signing's experience will prove valuable to his team, while praising the recently retired Swede international.
"Zlatan needs no introduction. The statistics speak for themselves. Ibra is one of the best strikers in the world and a player who always gives 100 per cent," added Mourinho.
"He has won the most important league championships in the world of football, now he has the opportunity to play in the best league in the world and I know he will grasp this opportunity and will work hard to help the team win titles.
"I am certain that his talent will delight fans at Old Trafford next season and that his experience will be invaluable in helping to develop the younger players in the squad."
Ibrahimovic will look to make his official Premier League debut when United face Bournemouth in their season opener on 13 August.
