The Germany international, who spent last season on loan at Sevilla, is again seeking regular first-team football having been deemed surplus to requirements at Stamford Bridge
Reports suggest the Germany international will pen an initial loan deal at Stadio Artemio Franchi, having failed to gain regular first-team action at Stamford Bridge.
"Pending official confirmation [of the transfer], Marin is undergoing a medical," read a post on Fiorentina's official Twitter profile.
Marin signed a five-year contract at Chelsea in 2012 but has made under 20 appearances for the Blues since making his initial move from Werder Bremen.
He spent the 2013-14 campaign on loan at Sevilla, winning the Europa League, and it now appears that the 20-year-old will link up with Vincenzo Montella's side.
Marin made 18 appearances in Spain's top flight last season, but missed part of the campaign with a thigh complaint.