Goal can confirm that Cavani, who has been without a club since leaving PSG upon the expiration of his final contract in June, will sign a one-season deal with the option of a second year with the Red Devils on deadline day.
The 33-year-old could pocket an extra €2m in bonuses at Old Trafford and will receive a €4m premium once the transfer is finalised.
Cavani will earn slightly less at United than he did at PSG, but significantly more than he would have had he chosen to join Atletico Madrid.
Goal has learned that the Uruguayan had an offer of €9m (£8m/$10.5m) per season on the table from Atletico where he could have linked up with fellow countryman Luis Suarez, who moved to Wanda Metropolitano from Barcelona last month.
The prospect of playing under Diego Simeone at Madrid held great appeal to Cavani, but he has ultimately chosen to join the Red Devils due to the superior financial package on offer.
Atletico were unable to match United's bid after exceeding the staff cost limit amid the coronavirus crisis in La Liga, and would first have had to find a buyer for Diego Costa to free up extra funds.
Cavani is now looking forward to joining up with his new team-mates at Old Trafford, with his arrival set to be confirmed subject to a medical on Monday.
The experienced striker has long been revered as one of the most deadly marksmen in European football, having also had successful spells at Napoli and Palermo.
He took his game to new heights at PSG, scoring 200 goals in 301 appearances to become the club's record scorer, while also getting his hands on 19 trophies including six Ligue 1 titles.
Cavani will join a United side in desperate need of inspiration following a poor start to the new season, and who suffered a humiliating 6-1 defeat at home to Tottenham on Sunday.
The Uruguay international could be in line to make his debut for the Red Devils after the international break, with a trip to St James' Park to face Newcastle on the cards on October 17.