Hannant's earliest credited work is as a director: in 1970, Hannant and seven other directors (Frances Beaton, Arch Nicholson, Richard Brennan, Ian Dunlop, Kit Guyatt, Chris McCullough, Malcolm Smith, and Doug White) collaborated on Or Forever Hold Your Peace: A Film of the Vietnam Moratorium, Sydney for the Experimental Film and Television Fund.
He followed this in 1971 with a contribution to the tripartite film Three to Go (1971): Hannant wrote and directed the segment 'Judy' (with additional dialogue by Bob Ellis), while the other two segments were written and directed by Oliver Howes ('Toula') and Peter Weir ('Michael'). Hannant was also assistant director on Weir's segment 'Michael', just as he had been assistant director on Weir's Homesdale (1971).
In 1972, he wrote and directed Flashpoint, a relatively short film (fifty-six minutes) starring Serge Lazareff, Wyn Roberts, and Janet Kingsbury. Describing the film (produced by Gil Brealey) as both romance and social realism, Screen Australia provides the following synopsis:
'David, a fresh-faced new worker at the iron mine, discovers that his friend, Foxy, confident, assured on the job, is really insecure, uncertain of himself and of his attractive wife Vicky. In an isolated mining town where there are 50 single men to a single woman, the human flashpoint is set low. The miners are an explosive force and the woman - one woman, Foxy's wife, is the fuse. Many men have been wary of igniting it but, without realising what he is doing, it is David who eventually provides the spark.'
For the above films, Hannant was working for the Commonwealth Film Unit (now Film Australia). In the late 1970s and 1980s, he left Film Australia and wrote, produced, and directed documentaries for the South Australian Film Corporation.
In the early 1980s, Hannant returned to Sydney for Mad Max 2, which he co-wrote with Terry Hayes and George Miller: the script was nominated for a Saturn Award for Best Writing (1983) and a Hugo Award for Best Dramatic Presentation (1983). Hannant was also first assistant director and second unit director on the production.
In 1983, Hannant directed the documentary Kakadu, which covered the history of Kakadu National Park.
Hannant's final credit was 1987's The Time Guardian, starring Tom Burlinson as a man struggling to protect the dying human race from their beast-like alien overlords.
During the 1990s, Hannant was Head of Directing at the Australian Film Television and Radio School for five years. More recently, he has worked in the screenwriting section of the Sydney Film School.