This paper examines the work of Gordon Stephenson between January 1942 and December 1947 when he worked for the British central planning ministry. Using public and his own personal archives, it shows how, as part of a small, very talented team, he played a key role in developing a new expertise of planning to address the great challenges of the post-war years. The paper discusses his work formulating new planning standards for residential and commercial densities, daylighting and community development. He also played a significant role in Patrick Abercrombie's Greater London Plan team and led the small group that subsequently planned what became the first New Town at Stevenage. The paper shows that, at this time, Stephenson saw the planner as a rational, technical expert rather than as a consciously political actor.