Sir John Nicholl (16 March 1759 – 26 August 1838) was a Welsh Member of Parliament and judge. As a judge he was noted "for inflexible impartiality and great strength and soundness of judgement".^[1]

Nicholl was born in 1759, the second son of John Nicholl of Llan-maes, a small village near Llantwit Major in Wales. He was educated at Cowbridge and Bristol Grammar Schools, before gaining entry to St John's College, Oxford, in 1775. He graduated as Bachelor of Civil Law in 1780 and as Doctor of Civil Law in 1785. He was called to the bar of the Doctors' Commons in 1785.^[2]

Nicholl built an extensive practice and on 6 November 1798 he succeeded Sir William Scott as King's Advocate and was knighted as was custom for the position. Within this role, Nicholl would often brief the Privy Council and Secretary of State on international law.

In 1802, Nicholl was elected to Parliament holding the seat of Penryn in Cornwall. After a brief period as Member of Parliament of Hastings from 1806 to 1807, he was elected to the seat of Great Bedwyn, and remained the member of the constituency until the Reform Act of 1832, upon which time he retired.^[3] Nicholl was a staunch Tory throughout his political career and steadily opposed parliamentary reform and Roman Catholic emancipation.

In 1809 he was appointed Dean of the Arches, was admitted to the Privy Council and became a judge of the Prerogative Court of Canterbury. In this capacity, he decided the much quoted case of White v Driver. In 1833 Nicholl was appointed as Judge of the High Court of Admiralty and held the post until his death in 1838;^[4] though he resigned his offices as Dean of Arches and in the Prerogative Court after he was made vicar-general to the Archbishop of Canterbury's court in 1834. For his work during the Napoleonic Wars, as a member of the volunteer movement, he was awarded the rank of lieutenant-colonel.

Nicholl was a Fellow of the Royal Society and of the Society of Antiquaries. A monument to John Nicholl son of Sir John Nicholl is to be seen in the Dyfrig chapel of Llandaff Cathedral.

Despite spending much of his time in London, linked to his parliamentary and judicial duties, and the fact that Nicholl held all his political seats in England, he continued to foster and support links with his home country of Wales. In 1787 he married Judy Birt, the youngest daughter of Peter Birt of Wenvoe Castle, and spent his time during his political career split between his London town house and Tondu House in South Wales.

Nicholl and Judy had one son and three daughters. Nicholl's only son, also John Nicholl, would later follow his father's political career, becoming a Member of Parliament for Cardiff.