McManus was born in Hamilton, Lanarkshire, Scotland, on 21 February 1935. Mark was moved to Hillingdon, Uxbridge, in London when he was three years old until he moved again at the age of 16 to Australia where he performed in amateur theatre groups which led him to become a professional actor. He appeared in the popular children's TV series Skippy the Bush Kangaroo, and made a guest appearance in the long-running Australian police drama Homicide. He also starred in Tim Burstall's unsuccessful but historically important feature film 2000 Weeks (1969), which was the first full-length Australian-produced feature made in Australia since Charles Chauvel's Jedda in 1954.
McManus also appeared in the American-produced historical drama Adam's Woman (1970) and co-starred with Mick Jagger in the unsuccessful Tony Richardson 1970 film version of the Ned Kelly story, Ned Kelly.
McManus returned to the UK in 1971 and came to wider attention playing roles such as Harry Carter in The Brothers, and Sam Wilson, a coal miner in the 1973 TV series Sam. He appeared opposite Peter O'Toole in the 1976 TV movie Rogue Male, and starred as a dour Scots police officer, Jack Lambie, in Strangers, a role he reprised as a guest star in the spin-off, Bulman. He also had roles in productions at the National Theatre and the Royal Court Theatre.
McManus was also a boxer before acting. He is not to be confused with the boxer of the same name (born 1974) from Basildon in England.
McManus began playing the title character in the crime drama Taggart in September 1983 alongside Neil Duncan, Tom Watson and Robert Robertson. The pilot attracted an estimated 7.6 million viewers. When Duncan left the show in 1987, James MacPherson joined the show as the new character Michael Jardine. This was followed by new Superintendent Jack McVitie in the 1985 episode "Murder In Season". A new female Detective Constable, Jackie Reid, was introduced in 1990 and, in "Rogue's Gallery", (1990) Taggart promoted her to Detective Sergeant.
After the death of McManus in 1994, his character was given an on-air funeral in the final episode of the series' 11th season, "Black Orchid". In that same episode, the character of Michael Jardine, portrayed by actor James MacPherson, was promoted to Taggart's position of Detective Chief Inspector.
His final Taggart episode was "Prayer for the Dead" (1995). McManus was the first Taggart cast member to die followed by Iain Anders (Jack McVitie) who died three years later in 1997 aged 64 from a sudden heart attack.
