John Denis Leonard, Baron Leonard, OBE (19 October 1909 – 17 July 1983) was a British Labour Party politician.
Leonard was born in Manorhamilton, Ireland, the son of an Irish journalist.
He emigrated to the United Kingdom in 1939, where he set up an engineering firm in Cardiff.
On 2 May 1978, Leonard was made a life peer, as Baron Leonard, of the City of Cardiff in the County of South Glamorgan.
He was selected as High Sheriff of South Glamorgan for 1979, but was excused from serving upon his elevation to the peerage.