The Serbian-born German international, 25, has struggled to force his way into the first team under successive managers at Stamford Bridge.
Marin joined the Blues from Werder Bremen on a five-year deal in the summer of 2012 but played only 16 times during a difficult first season under Roberto Di Matteo and then Rafael Benitez.
He was allowed to join Sevilla on a season-long loan last term and won the Europa League with the Spanish club whilst making 28 appearances in all competitions, but failed to score.
He is likely to come up against former Chelsea team-mate Ashley Cole in his first game against Roma, after the defender moved to Serie A in the summer.
Marin began his career at Borussia Mönchengladbach before in 2009 joining Werder Bremen, where he made over 100 appearances and scored eight goals in the Bundesliga.