The Sweden striker is set for medical testing on Friday after verbally agreeing terms of his one-year deal weeks ago, with wages thought to be in excess of £200,000 a week.
Ibrahimovic posted a picture of the Manchester United badge alongside a caption reading: 'Time to let the world know.' He finished the post with the message '#iamcoming'.
The former Barcelona and Inter Milan frontman has allowed his contract at Paris Saint-Germain to run down when it became clear Mourinho would replace Louis van Gaal at Old Trafford.
He will officially put pen to paper on Friday as he becomes Mourinho's second signing since taking charge, a development which will still guarantee the striker a bonus payment from PSG.
Ibrahimovic has painfully attempted to keep supporters guessing over the last month, his agent Mino Raiola even suggesting earlier in the day no decision on his future had been made. In reality, he is thought to have been checking out properties in Cheshire in readiness of the switch.
Mourinho was always keen on a reunion after spending time with Ibrahimovic at Inter Milan and the new manager wants to add further attacking options after a lifeless year under Van Gaal.
United are desperate to add Borussia Dortmund playmaker Henrikh Mkhitaryan with a bid in excess of £30million hoped to tempt his club into selling.
Ibrahimovic, meanwhile, will link up with United's squad in the coming weeks as they prepare for the first season under Mourinho.
Stars who participated in Euro 2016 and the Copa America will be afforded extra time off before their tour of Asia, which they are due to fly out for on July 19.
Mourinho faces Dortmund and Manchester City before Ibrahimovic is given the chance to show off in his homeland when they take on Galatasaray in Gothenburg on July 30.
-Daily Mail
