Leoline Jenkins was born in Llantrisant, the son of a small landowner. He went to school in the nearby town of Cowbridge and then proceeded to Jesus College, Oxford.
As Judge of the Admiralty Court from 1665, played a crucial role in the development of English Admiralty law as a coherent body of legal principles. He served Charles II as Secretary of State. He secured the passage of the Statute of Distributions dealing with intestacy (1670) and was one of the drafters of the Statute of Frauds 1677. Sir Leoline also represented the King in international private law cases as well as serving as a diplomat. He was the Principal of Jesus College, Oxford and bequeathed an endowment by which the Welsh character of the college was still further accentuated.
Sir Leoline spoke fluent Welsh, and was fond of quoting Welsh proverbs, sometimes to the bewilderment of his listeners.