Mallaby made his acting debut at the
Adelaide Festival of Arts, but soon obtained TV roles in Melbourne. He played Detective Peter Barnes in the crime series
Homicide in episodes 131 to 395 from 1967 to 1973, representing more than half the series run. Along with
Alwyn Kurts,
Leonard Teale and
Norman Yemm, Mallaby was part of what is often considered "the consummate
Homicide cast". He also wrote scripts for the series, some under his first wife's name. After
Homicide he was an original cast member of
The Box in the lead role of television executive Paul Donovan, staying in the role from 1974 until 1975. He was later an original cast member of
Cop Shop as head of a suburban police station's
Criminal Investigation Branch, Detective Senior Sergeant Glenn Taylor. He continued in that role from the program's debut in November 1977 until 1979. In 1980 he appeared in
Prisoner for several months as social worker Paul Reid. He also wrote scripts for
Prisoner and
Matlock Police. He said of scriptwriting that "writing requires a mood. It might be called a creative mood, I suppose. Unfortunately for those close to me, the mood often seems to come around 4 am. I get a spasm of creativity and just have to jump out of bed and start writing". Mallaby also acted in mini-series including
Power Without Glory,
Sword of Honour and
All the Way. He acted in feature films such as
Tim Burstall's
Eliza Fraser (1976),
Petersen, and
End Play. During the late 1970s he returned to
Britain. There he made appearances in various television series including
Secret Army,
Survivors and
The Professionals, and appeared as a submarine crew member in the
James Bond film
The Spy Who Loved Me (1977). His last regular role was as
Colonel Mustard in
Cluedo, the game show-comedy-mystery series. ==Awards==