Allan Maconochie, the Scottish judge, was born on 26 January 1748. He was the son of Alexander and Isabella Maconochie, Meadowbank Estate, Kirknewton (now in West Lothian), to the west of Edinburgh. He was privately educated by Dr. Alexander Adam (1741-1809) who later on became Rector of the Royal High School in the city. Maconochie then studied at Edinburgh University taking the classes of Adam Fergusson, Professor of Moral Philosophy, and Hugh Blair, Professor of Rhetoric and Belles-Lettres. He also studied Roman Law with the Professor of Civil Law, Robert Dick, from 1766 to 1769. He was then apprenticed to Thomas Tod, a well-known Writer to the Signet. During this period he co-founded the Speculative Society, an institution which 'trained' young men in 'public speaking, talent, and liberal thought'. On the conclusion of his studies in 1768, he went to Paris for a short time. In 1770 he became an Advocate and in Spring 1771 was admitted as a student of Lincoln's Inn, though he was never called to the English Bar. In 1773, he returned to France.

On 11 November 1774, Maconochie married Elizabeth Welwood, a daughter of Robert Welwood of Garvock and Pitliver, Fife, and grand-daughter of Sir George Preston of Valleyfield. Also in 1774 he was elected to the General Assembly as a lay representative of the Burgh of Dunfermline.

On 16 July 1779 Maconochie was appointed Professor of Public Law and Law of Nature at Edinburgh University, and also in 1779 he was elected Treasurer of the Faculty of Advocates. At the University, he advertised classes each year until he resigned the Chair in 1796. In 1788 he became Sheriff-Depute of Renfrewshire, and in 1796 he succeeded the judge and essayist Alexander Abercromby, Lord Abercromby (1745–1795) as an ordinary Lord of Session taking his seat on the Bench on 11 March as Lord Meadowbank.

Maconochie had also been a keen agriculturalist and he wrote anonymously theDirections for preparing manure from peat, and instructions for foresters(1802) which was reprinted in 1815 and 1842. Other publications includedConsiderations on the introduction of jury trial in civil cases into Scotland(1814) andEssay on the origin and structure of the European legislatures(1788). A portrait of Maconochie was said to have been painted by Sir Henry Raeburn in 1814.

Allan Maconochie, Lord Meadowbank, died at Coates House, near Edinburgh, on 14 June 1816. He was buried in the private burial-ground on the Meadowbank Estate, Kirknewton. At his death he had been a Senator of the College of Justice, one of the Lords Commissioners of Justiciary, a Lord Commissioner of the Jury Court, and Vice-President of the Royal Society.

Lord and Lady Meadowbank had four sons - the Scottish judge Alexander Maconochie-Welwood (1777-1861); Robert Maconochie (d. 1858) who became Mint Master in Madras, India; James Allan Maconochie (d. 1854), Sheriff of Orkney and Shetland; and, Thomas Tod Maconochie (d.1847). Alexander Maconochie-Welwood was also painted by Raeburn in 1816 and this portrait is owned by the Metropolitan Museum of Art in New York, USA.