Son of Leonard and Louisa (nee James) Northcroft, who emigrated to Wellington from Victoria, Australia.

Northcroft began practicing law in Hamilton in 1907.

On 2 December 1908 (his 24th birthday), he married Violet Constance Mitchell at St Mary's Cathedral in Auckland. They had two daughters.

Northcroft was promoted to Major and appointed Officer Commanding (OC) of 1 Battery, New Zealand Field Artillery (NZFA), on 1 February 1918.

Member of the Auckland University College Council, 1924-35

He was appointed a Judge with the Supreme Court of New Zealand, Christchurch, in 1935.

During WWII, he served as the Directory of Artillery, Southern Military District, and Fortress Commander for the Lyttelton-Sumner area, Christchurch, 1940-45.

Served as the New Zealand Judge at the International Military Tribunal for the Far East in Tokyo, Japan, 1946-48. For his services with the Tribunal he was awarded a knighthood in 1949.

Attended Auckland University College (now the University of Auckland). AWMM