He started his League of Ireland career in 1988 when he was signed by Brian Kerr for St Patrick's Athletic from junior side Mount Merrion.

He struggled to make an impact during his first season but made his league debut on 3 September 1989 in Limerick after Robbie Gaffney broke his leg.

His goal for St Pats away to the then champions Derry City FC is said to have been the turning point of that season and the Saints went on to win their first league title since 1956, with Osam playing an influential role as a left winger despite his six-foot four frame.

The treatment he received from the board of Shamrock Rovers led to Osam leaving after just one season after two goals in 21 total appearances.

He played in central midfield and, along with Eddie Gormley and Noel Mernagh, was the driving force behind another league title.

With the disruption caused by Brian Kerr leaving to take charge of the Irish underage teams, the 1996–97 was out of reach for St. Pats.

Throughout his career, Osam was heavily pushed for inclusion in the Republic of Ireland national football team.

Osam is married and has a son Evan who is a former Republic of Ireland youth international and plays for Bray Wanderers.