The two clubs have already conducted business this summer, with Stefan Savic leaving the Serie A side to move to the Spanish capital and now Suarez will go the other way.
"Mario Suarez will play for Fiorentina," reads a statement on their official website. "The agreement between clubs is complete and the move will be made formal in the coming hours.
"The midfielder has traveled with permission of the club to join the Italian side."
Suarez came through Madrid's youth system and emerged in the first team before going out on loan to Valladolid and Celta and then joining Mallorca for two seasons.
He then returned to the Rojiblancos in 2010 and went on to win the Europa League, La Liga and the Copa del Rey, reaching the Champions League final with Diego Simeone's men too.
Suarez is the latest high profile departure from the Vicente Calderon club, following Mario Mandzukic, Arda Turan, Miranda and Toby Alderweireld out the door, while Jackson Martinez, Luciano Vietto, Yannick Ferreira Carrasco and Savic have been brought in.