Cohen was appointed to the High Court in 1943 and assigned to the Chancery Division, receiving the customary knighthood.

On 12 November 1951, he was appointed Lord of Appeal in Ordinary and made additionally a life peer with the title Baron Cohen, of Walmer in the County of Kent.

Cohen chaired many Royal Commissions in the years following World War II, particularly the Report of the Committee on Company Law Amendment in 1945 and on compensation.

[3] From 1946 to 1956 he chaired the Royal Commission on Awards to Inventors, which acknowledged scientists who had made technological advances such as radar and the jet engine during the war.

Tim's son, Sir Jonathan Cohen, was a High Court judge.