De Marchi started his career with the Como youth system, and was successively sold to Serie C2 club Ospitaletto, where he made his professional debut. In 1987, he followed his head coach Luigi Maifredi at Serie B fallen giants Bologna, being protagonist of the team's promotion to the top flight and the successive campaign that led the rossoblu back into European football.
In 1990, he followed Maifredi once again, joining Juventus. After an unimpressive debut season, he was successively loaned out to AS Roma for the 1991–92 season. After a season back at Juventus where he played in the first leg of the victorious 1993 UEFA Cup Final, De Marchi successively agreed for a comeback to Bologna in May 1993, becoming also the team captain and playing there for four more seasons, his last ones as a footballer in Italy. In 1997, he agreed for a move abroad to Eredivisie side Vitesse Arnhem, and in 2000 he went to Dundee with little success before to retire from active football in 2002.