Educated at Eton and at St. John's College, Cambridge, he entered the House of Commons in 1813 and the House of Lords as a baron following his father's death in 1818. He served as lord privy seal in 1828 and was president of the Board of Control for India in 1828–30 and for brief periods in 1834–35 and 1841. In the latter year Ellenborough was appointed governor-general of India. He had opposed since 1839 the costly intervention in Afghanistan, and after the First Afghan War he decided to make the Indus River his frontier, retaining only those strongpoints upon it which ensured free navigation. However, rash opportunism led him to acquiesce in actions of Sir Charles James Napier (Napier, Sir Charles James), his governor in Sindh (Sind), which drove the Sindhi emirs (rulers) into war and defeat (1843).

Ellenborough then pursued his plans to promote trade by ending tolls and duties throughout Sindh and Bahawalpur (both now in Pakistan), the North-Western Provinces, Madras (now Chennai), and Bombay ( Mumbai). But a war with Gwalior in December 1843, designed to keep its large army out of hostile hands, frustrated these plans, and the directors, exasperated by Ellenborough's arrogant self-will, resolved in April 1844 to recall him. On his return he was created an earl and viscount.

Ellenborough served under Sir Robert Peel as first lord of the Admiralty in 1846 and under Lord Derby at the Board of Control in 1858. There he drafted the new plan for the government of India, which the Indian Mutiny (1857–58) had rendered necessary, but, by making public a caustic dispatch censuring Lord Canning's Oudh proclamation, which Ellenborough thought betrayed a desire for indiscriminate vengeance, he roused such opposition that he chose to resign. He never held office again.