They will pay a reported €500,000 (£445,000, $579,000) - subject to a medical - to take him on loan for the duration of the 2018-19 season, and should they wish to retain his services, he will cost a further €7 million (£6.2m/$8m).
“Fiorentina wish to announce that we have acquired, on a temporary basis with the right to retention, the rights to the sporting performances of footballer Kevin Mirallas from Everton,” a statement from the Italian side read.
“Mirallas was born on October 5, 1987 in Liege, Belgium, and will sign a contract that will tie him to Fiorentina for the next four seasons.
“The player will be in Florence in the next few days for a medical.”
Having signed for Everton from Olympiacos in 2012, the 30-year-old had rather fallen out of favour last season at Goodison Park, where he made only five Premier League appearances. In January, he was moved on loan back to Olympiacos, where he scored two league goals in 13 outings.
The arrival of Richarlison over the summer has seen him fall further down the pecking order under Marco Silva, and he now looks set to end his time on Merseyside.
Previously, the 60-time capped Belgium international has turned out for Saint-Etienne and Lille in Ligue 1, though it was during his previous two-year spell in Greece that he really flourished, netting 34 times in only 52 outings.
His best goalscoring season for Everton saw him find the target eight times in 32 appearances during the 2013-14 campaign.