Basil Montagu (24 April 1770 – 27 November 1851) was a British jurist, barrister, writer and philanthropist. He was educated in Charterhouse School and studied law in Cambridge, later wrote and worked on reforms in bankruptcy laws of Britain. He served as Accountant-General in Bankruptcy between 1835 and 1846. He was highly influenced by the writings of Francis Bacon. He was the son of John Montagu, 4th Earl of Sandwich, and his mistress, singer Martha Ray.
He was the second illegitimate son of John Montagu by Martha Ray; he was acknowledged by his father, and brought up at Hinchingbrooke, Huntingdonshire. He was educated at Charterhouse School and Christ's College, Cambridge, where he matriculated in 1786, graduated B.A. (fifth wrangler) in 1790, and proceeded M.A. in 1793. On 30 January 1789 he was admitted a member of Gray's Inn, but continued to reside at Cambridge until 1795, when, having by a technical loophole lost the portion of inheritance intended for him by his father, he came to London to read for the bar.
He was on intimate terms with Samuel Taylor Coleridge and William Wordsworth, whose early enthusiasm for the ideas of the French Revolution he shared. In the autumn of 1797 he made a tour in the Midlands counties with William Godwin. He spent a week in Godwin's house in 1797, assisting the distraught Godwin, whose wife Mary Wollstonecraft was dying, following the birth of a daughter.
He was called to the bar on 19 May 1798. By Sir James Mackintosh, whose acquaintance he soon afterwards made, and with whom he went the Norfolk circuit, he was converted to political moderation and the study of Francis Bacon. Montagu was also a friend of Samuel Parr. Montagu never became eminent as a pleader, but he gradually acquired a practice in chancery and bankruptcy; his leisure time he devoted to legal and literary work.