A Norths Ipswich Tigers junior, Mercy made his first grade debut for Parramatta in Round 7 of the 1995 ARL season, coming off the bench in a 4–40 loss to the Auckland Warriors at Parramatta Stadium. He played 9 games for Parramatta in his debut season, which were all losses as the club finished second last. At the end of 1995, Mercy was released by the Eels as the club was looking to rebuild.[2][3]
In 1996, Mercy played for the Atherton Roosters in the Cairns District Rugby League.
In 1997, Mercy joined the North Queensland Cowboys. That season, Mercy scored six tries in six games spending the majority of the season in reserve grade. In 1998, Mercy played his first full season of first grade, playing 24 games and scoring 12 tries for the Cowboys. In Round 2 of the 1998 season, Mercy scored four tries in a 26–2 win over the Balmain Tigers, setting the club record for most tries in a game, which still stands as of 2020. At the end of the season, he was released by the Cowboys.[4]
In 2001, Mercy played for the Ipswich Jets in the Queensland Cup.[5] In 2006, he switched codes to play rugby union with Grafton in northern New South Wales, after playing for a number of different local rugby league teams over the years, including the Booval Swifts, Lower Clarence and South Grafton.[6][7][8][9] In 2019, he coached the Lower Clarence Magpies.[10]
