His father was Raymond Postgate and his mother Daisy Lansbury, making him the grandson of Labour politician, George Lansbury; some of whose principles he inherited, to the extent that he was prepared to go to prison as a conscientious objector during World War II. As his father had done, in 1916.
Subsequently he did a number of different jobs, never really finding his niche until he entered into a collaboration with Firmin, who built most of the models used in the various animations. Setting up their business in a disused cowshed, Postgate and Firmin worked on children's programmes based on concepts and scripts which mostly originated with Postgate. He was also the narrator for all the Smallfilms productions, and his distinctive voice became familiar to generations of children.
His autobiography, Seeing Things, was published in 2000.