Northbrook entered upon a political career, and was successively private secretary to Henry Labouchere (Board of Trade), Sir George Grey (Home Office), and Sir Charles Wood (India Office and then Admiralty to 1857). In 1847 he served on the committee of the British Relief Association. In 1857, he was returned to the House of Commons for Penryn and Falmouth, which he represented until becoming a peer on the death of his father in 1866. He served under Lord Palmerston as Civil Lord of the Admiralty between 1857 and 1858, as Under-Secretary of State for War in 1861, as Under-Secretary of State for India between 1861 and 1864, under Palmerston and Lord Russell as Under-Secretary of State for the Home Department between 1864 and 1866 and under Russell as Secretary to the Admiralty in 1866.