While playing football, Farrell was employed in the New South Wales Police Force in a career that lasted from 1938 to 1976. During his long tenure as sergeant of the 21st Division Darlinghurst (Kings Cross) police station in Sydney he was outwardly respected as an honest and tough member of the community and police force as a member of the Vice Squad. Farrell became one of Sydney's most famous Policemen and was featured in hundreds of media reports between the 1940s and the mid-1970s. His highest rank was Inspector 1st Class.