D'arcy, who is a product of Marr College, has played for Kilmarnock, Marr RFC and Whitecraigs.
He spent loan periods with Treviso and London Scottish in season 2014-15.
He made his Warriors debut off the bench against Munster.
D'arcy said: "I'm proud to have signed my first professional deal with the club, after making my debut against Munster.
"Playing for Benetton Treviso is a great experience for me and I'm happy to have returned to Italy until the end of the season.
"I've been made to feel very welcome in Treviso and by extending my loan period it will hopefully enable me to continue to get regular game time at a high level, before returning to Glasgow in the summer."