 During the Second World War he worked in the Ministry of Supply in Washington DC and on the Board of Trade.In 1947, he succeeded
James Meade as the Director of the Economic Section of the Cabinet Office of the British government; from 1953 until 1961 he was chief economic advisor to successive Chancellors of the Exchequer.Hall was appointed a Companion of the Order of the Bath (CB) in the 1950 New Year Honours, he was appointed a Knight Commander of the Order of St Michael and St George (KCMG) in the 1954 New Year Honours.