Cavani, 33, became a free agent over the summer after a seven-year stint with the Paris club.
It's been a busy day for United, with the club also reportedly securing a €40 million transfer million for Atalanta's 18-year-old winger Amad Diallo Traore, per Laurie Whitwell of The Athletic, and a €17 million transfer for Porto left-back Alex Telles, per Charlotte Duncker of Goal.
As for Cavani, on Sunday, Rob Dawson of ESPN provided more details on his addition:
"United turned down the chance to sign Cavani in January after being put off by his wage demands of £360,000-a-week. After leaving Paris Saint-Germain in the summer, the striker has been offered to every major club in Europe before United stepped up their interest last week.
"Sources have told ESPN his wages will be significantly lower than his demands in January and the agent fees involved in the deal will be lower than €10m."
While Cavani is no longer in his prime or the player who posted 35 goals in league play during the 2016-17 season and 28 league goals in 2017-18, he'll provide solid depth at the striker position for Man United.
Cavani released the following statement after officially signing, per Sam France of Goal:
"Manchester United is one of the greatest clubs in the world, so it is a real honour to be here. I've worked really hard during the time off and I feel eager to compete and represent this incredible club. I have played in front of some of the most passionate supporters in football during my career and I know that it will be the same in Manchester. I cannot wait to experience the Old Trafford atmosphere, when it is safe for the fans to return."
He'll provide both excellent cover for starting No. 9 Anthony Martial and a different type of forward, giving Ole Gunnar Solskjaer some lineup flexibility with his front line going forward.