He was called to the bar by the Inner Temple in 1905, developing first a good general practice, then specialised in work in the Commercial Court.

[10]Though Porter did not have a high public profile, he came into prominence in 1936, when he chaired a tribunal of inquiry (whose other members were Gavin Simonds, KC and Roland Oliver, KC) appointed to investigate "whether any unauthorized disclosure was made of information to the Budge for the present year, or any use made of any such information for the purposes of private gain.

"[1][10] As a result of the tribunal's report, the Labour minister J. H. Thomas resigned as Secretary of State for the Colonies, as did Sir Alfred Butt, MP.

The same year, he issued a bench warrant against the vaudeville actress Peggy O'Neil for failing to answer a subpoena.

[13] Porter sat on the appeal of William Joyce, commonly known as "Lord Haw-Haw", who had been convicted of treason for his war-time propaganda broadcasts from Nazi Germany, and dissented from the majority.

[14] He also dissented in National Anti-Vivisection Society v Inland Revenue Commissioners (1948), a leading case concerning charitable trusts.

[1][10][16] Porter resigned as Lord of Appeal in 1954 because of ill-health, having been promoted to be a Knight Grand Cross of the Order of the British Empire (GBE) in the 1951 New Year Honours.

During the Second World War, Lord Porter's flat in London was bombed, leading him to move to Emmanuel College, Cambridge, which had elected him an honorary fellow in 1937.

[1] He lived there for the remainder of his life, commuting to London by train and attending services at St Columba's Presbyterian Church, where his mother had worshipped.