Villa did not disclose the duration of the 24-year-old's contract or the transfer fee, but media reports said it was a five-year deal worth 35 million euros.
Guessand graduated from Nice's youth system and made his senior debut in 2020. He went on loan to Swiss club Lausanne-Sport and French side Nantes before having his best season yet in 2024/25, scoring 12 goals in Ligue 1 as Nice finished fourth.
He also scored his first goal for the Ivory Coast in March in a 1-0 win over Morocco in the World Cup qualifiers.
"When I heard (Villa) wanted me, I didn't think twice. I'm ready to give my all," Guessand said in a video posted on social media by the English club.
Villa, who finished sixth last season, begin their league campaign with a home game against Newcastle United on August 16th.