Lord Ellenborough, one of the most formidable lawyers of his age, was born at Great Salkend, the fourth son of Edmund Law (1703-1787), Bishop of Carlisle, and his wife Mary, daughter of John Christian of Ewanrigg, Cumberland. Educated at Charterhouse and later Peterhouse, Cambridge, Law was admitted as a student at Lincoln's Inn on 10 June 1769. By 1775 he had successfully established himself as a special pleader and five years later he was called to the Bar on the same day as William Pitt.
Law rapidly acquired a large practice, and in 1787 was made a King's Counsel. On the advice of Sir Thomas Rumbold, who had married his youngest sister, Joanna, he was retained as the leading counsel of Warren Hastings, in whose defence he was to make his name; his opening speech for the defence, which lasted three days, was widely considered to have been masterly. A succession of other high profile legal cases paved the way to his appointment as Attorney General in 1801, and almost immediately afterwards he was knighted by King George III. In the same year Law was returned as Member of Parliament for the borough of Newton on the Isle of Wight. He had only been in the Commons, however, for a year before he was appointed Lord Chief Justice of England, and on 19 April 1802, he was created Baron Ellenborough of Ellenborough in Cumberland.
Ellenborough involved himself in many of the most contentious political issues of his day; he expressed his strong opposition to the political emancipation of Roman Catholics in 1805, and the following year he supported the Slave Importation Restriction bill. Among other high profile cases, he presided over the celebrated trial of Thomas, Lord Cochrane, later 10th Earl of Dundonald, in 1814, in a case of conspiracy to defraud the Stock Exchange. Cochrane was found guilty, but had such excessive punishments laid upon him, that Ellenborough's house was attacked in protest. By 1816 Ellenborough's health had begun to deteriorate, and having retired his post of Lord Chief Justice, he died on 13 December 1818.
He married, in 1789, Anne, daughter of Captain George Phillips Towry, whose beauty was such that passers-by were said to linger by her house as she watered the flowers. She also sat to Lawrence for a smaller format portrait (29 x 24½ in.) which was exhibited at the Royal Academy in 1813 (see K. Garlick, op.cit., 1989, no. 270). The sitter and his wife's decision to commission portraits from Lawrence may have been influenced by the success of the artist's earlier portrait of Ellenborough's elder brother, Ewan, who was also a Member of Parliament, which was painted in the mid-1790s (see K. Garlick, op.cit., 1989, p. 220, no. 467; Detroit Institute of Arts).
Ellenborough had thirteen children, seven sons and six daughters. His eldest son, Edward Law (1790-1871) became Governor-General of India, and his second son Charles Ewan was Recorder of London.