Tim spent a season with Glasgow - in 2005/06 - before re-joining Irish province Ulster for a season en route to French Top 14 side Castres.
On his return to Glasgow, 6ft 6in 18st Tim said: "I'm very excited to be coming back to Glasgow because I thoroughly enjoyed my previous spell with the club."
Tim played for Malone and Dungannon and has represented Ireland at U18, U19 and U21 levels.