He was a legal adviser to the Transvaal delegation to the 1908-1909 National Convention that drew up the Constitution for the Union of South Africa.

He was also a founder member of the Suid-Afrikaanse Akademie vir Wetenskap en Kuns ("South African Academy for Science and Art") in 1909.

As Chief Justice, he was required ex officio to act as Officer Administering the Government under a dormant commission, in the absence of the Governor-General, which he did for two and a half years, from the death of Sir Patrick Duncan in 1943 and the appointment of Gideon Brand van Zyl in 1945.

His first wife was Ella Scheepers, who is reputed to have composed the popular Afrikaans song Sarie Marais during the Anglo-Boer War.

His son by his first marriage, Dr. Quartus de Wet, was also a judge, and presided over the 1963 Rivonia Treason Trial of Nelson Mandela and other anti-apartheid activists.