Sexton was born in Auckland in 1892. He was educated at
Auckland Grammar School and later was admitted to
Auckland University where he graduated with a
Bachelor of Law in 1914. He then served in the army during
World War I where he was twice wounded (eventually losing a leg) and rose from the rank of private to that of captain. After the war, he attended law lectures in London and following being discharged from military service in 1918, he married Gladys Cicely Annie Astley (1891–1962), the granddaughter of suffragist
Annie Jane Schnackenberg. He passed his master's degree in laws with honours and also won the senior university scholarship in law for New Zealand in 1919. He then moved to
Manurewa and began practising law in Auckland. For a total of 14 years he served as president, vice-president and executive member of the Auckland
Returned Services Association. ==Political career==