The Catalan side announced Monday it has secured a loan deal for the Ghanaian forward until the end of the term, with an €8-million option to make the swap permanent in the summer.
Following reports earlier in the day surrounding the shock move, Boateng was the first to confirm that he was on his way to the Blaugrana.
"Barca, I'm coming!" he told Sky Sport's Fabrizio Romano at an airport in Italy. "I'm sad to leave Sassuolo but (it) is a great chance."
The 31-year-old has operated primarily as a lone striker for Sassuolo this season, scoring five goals in 15 appearances across all competitions, though he can also operate as an attacking midfielder.
He's likely to provide depth in Barcelona's front line behind the predominant starting trio of Lionel Messi, Luis Suarez, and Ousmane Dembele, though the latter is expected to miss the next two weeks after suffering a left ankle sprain Sunday against Leganes.
The move also marks a return to Spain for Boateng, who spent the 2016-17 campaign with Las Palmas. His quick La Liga stint proved, statistically, to be his best ever in a top domestic league, as he scored a career-best 10 goals in 28 appearances for the now second-tier outfit.
Boateng has been a journeyman since leaving Schalke for AC Milan in 2016. He departed the Rossoneri six months later for Las Palmas, but mutually agreed to terminate his contract with the club in the summer of 2017 ahead of a move to Eintracht Frankfurt.