John Copley, later Baron Lyndhurst, built his public career through law and parliamentary politics. Educated at Trinity College, Cambridge, he entered the bar and established a practice before joining the House of Commons in 1818. He became chief justice of Chester that year, solicitor general in 1819, attorney general in 1824, and master of the rolls in 1826. These appointments brought experience in courtroom advocacy, legal administration, and the government's parliamentary business.

In 1827 Copley entered the peerage as Baron Lyndhurst and became lord chancellor under George Canning. He retained the office under the succeeding ministries of Lord Goderich and the Duke of Wellington until 1830. As chancellor he presided in the House of Lords and exercised senior judicial responsibilities. He served as chief baron of the Exchequer from 1831 to 1834, returning to the chancellorship during the brief Conservative ministry of 1834–1835 and again under Robert Peel from 1841 to 1846.

Lyndhurst remained an influential Conservative speaker after leaving office. He had opposed the parliamentary reform proposals of 1831–1832, but his positions also reflected changes in party leadership and circumstances, including Peel's handling of the Corn Laws. In later life he spoke on foreign affairs and national defense, notably during the Crimean War and the invasion anxieties of 1859. He died in 1863. He should be distinguished from his father, the American-born painter John Singleton Copley.