Kerwick made his debut for South Sydney in Round 1 of the 1915 NSWRL season against Glebe at the Sydney Cricket Ground. The following season, Kerwick played at hooker in the 1916 grand finaldefeat against Balmain which ended 5–3. The following season, Kerwick was a member of the Souths side which finishedrunners up in the competition. In 1918, Kerwick played 13 games as Souths claimed the premiership that year but were not required to play in a grand final to be declaredpremiers. In 1919, Kerwick was selected to play for New South Wales and played featured in one match against Queensland. In 1920, Souths again finished as runners up in the NSWRL competition with Kerwick making 12 appearances. Kerwick played 2 more seasons for Souths and retired at the end of 1922.