He was a grandson of "the Welsh Swagman", Joseph Jenkins, whose voluminous Australian diaries over 25 years (1869-1894) he edited and published as excerpts in 1975
Evans was born in a Welsh farmhouse, "Tyndomen", near Tregaron, Ceredigion, the son of Ebenezer Evans and Elinor (Nell) Jenkins. His mother was a daughter of Joseph Jenkins, the "Welsh Swagman", who entrusted to her his manuscript Australian diaries.
He had two surviving older siblings, Elizabeth and Joseph, and two others who died as infants. His autobiography relates how he worked as a bank clerk from 1912 and enlisted for military service in 1914, serving with the Buffs and as an officer of the Lancashire Fusiliers at Ypres and Passchendaele Ridge, 1916-1918. After leaving France in September 1919, William Evans studied for University of London matriculation at the Aberystwyth University College and commenced medical studies at the London Hospital in 1920.
He graduated Bachelor of Medicine Bachelor of Science in 1925 and Doctor of Medicine in 1927.
He was appointed house physician to Sir John Parkinson at the hospital, later becoming his chief assistant in the Heart Department. He also assisted Lord Dawson of Penn in use of the electrocardiograph, with which he once favourably determined the disputed state of health of prime minister Stanley Baldwin.
Doctor Evans became an international authority and lecturer on diseases of the heart during his long career, from which he retired in 1967. He published several books and a large number of papers (an exhaustive list of which is appended to his autobiography).
In 1940, at age 45, Doctor Evans married Christina Downie (then aged 56).
There were no children and Christina died in 1964. In retirement he lived at Llanddewi Brefi where he was known as "Wil Blocks" because of a substantial concrete-block wall around his residence. He died in 1988 aged 92, at Withybush Hospital, Haverfordwest.
