The Architect's Department of London County Council was responsible for the development of London according to its own statutory plan. This entailed positive planning as well as controlling or vetting private development. The Department was under the leadership of the Architect to London County Council. Sir Robert Hogg Matthew was the first post-war Chief Architect (1946-1953), succeeded by Sir Leslie Martin (1953-1956) and then Hubert Bennet. It was the largest such local authority organisation in Western Europe, with 3000 staff in 1956.

Its design staff undertook a variety of jobs for London County Council departments, such as Housing, Parks, Schools and general civic improvements. From 1946-1949 the Architect's Department was made up of four main divisions: The Housing Division, the Schools Division, the Planning Division and the General Division.

The Housing Division was the largest and was itself served by a Housing Engineers Division, Structural Division and Quantities Division.

The Schools Division was a smaller group, with much design work contracted out to private architects. It had responsibility for maintenance, however.

The Planning Division was arranged into four sub-groups: Information and Research, the Development Plan Group, the Application Group and the Reconstruction Areas Group. Percy Johnson-Marshall was put in charge of the Reconstruction Areas Group when it was set up in 1949. At this time the Planning Division was under the directorship of Arthur Ling. In 1956 these groups were amalgamated into one single Policy Group for North East, North West and South London districts. Percy Johnson-Marshall was in charge of the North East group until 1959.

The General Division dealt with anything that was not Schools, Planning or Housing.