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.