He served as departmental secretary of the Attorney-General's Department from 1932 to 1946, and was then the inaugural Australian High Commissioner to South Africa from 1946 until his death the following year.
He was the son of Mary (née Cocks) and George Hopley Knowles; his father was born in Staffordshire, England, while his mother was a native Queenslander.
[2] Knowles was due to retire from the public service in March 1947 (his 65th birthday), but in April 1946 the federal government chose him as the inaugural Australian High Commissioner to South Africa.
[7] It was generally understood that Attorney-General H. V. Evatt pushed for the appointment so that he could install his own man, Kenneth Bailey, as departmental secretary.
[8] Knowles arrived in Durban in late July and was formally received by Governor-General Gideon Brand van Zyl on 3 September.
[17] In 1950, Lady Knowles donated money to the Council of the Canberra University College to provide an academic prize memorialising her late husband.