 His father, William "Bill" Mullins was an Australian representative who played 190 first grade games for Eastern Suburbs Roosters, and his uncle's Russell and Terry Mullins played for Sydney's Western Suburbs Magpies.Brett's son Bradley Mullins has recently signed with the Sydney Roosters, and is currently in their Holden Cup squad.Brett Mullins made his first grade début for Canberra from the substitution bench in a 48–0 rout of the South Sydney Rabbitohs in 1990.