The Frenchman has signed a three-year deal after joining for an undisclosed club-record fee.
"I think he will prove to be a great fit for us and the fact that he selected us above other options shows he's hungry to do well."
Welcome to the Blades, Lys ✍️ pic.twitter.com/1MZ1MajOJ7— Sheffield United (@SheffieldUnited) July 21, 2019
The 23-year-old started out at Le Havre, where he scored 14 goals in 34 outings.
He joined AFC Bournemouth in June 2016 and has since made 58 appearances in the Premier League for the south-coast side, scoring three times.
Mousset is United's fifth signing of the summer following the arrivals of Luke Freeman, Callum Robinson, Phil Jagielka and Ravel Morrison.
If he makes his debut for the Blades on the opening match of the season he will find himself in familiar surroundings as Sheffield United's opening match of the season is a trip to AFC Bournemouth on 10 August.