Gallagher began his career for North Sydney in 1950 and played two seasons for the club before signing with Souths in 1953.
In his first season at Souths, Gallagher was a member of the 1953 premiership winning team defeating St George 31–12.
The following year, Gallagher won his second premiership with Souths defeating Newtown 23–15 in the 1954 grand final.
In 1955, Gallagher won his third premiership with Souths defeating Newtown again by a score of 12–11 in the grand final.
Gallagher ended his illustrious spell with Souths in 1958 as the club failed to make the finals that year.