He was Foreign Secretary during 1828–30 and again from 1841 to 1846, when he concluded the Webster–Ashburton and Oregon Boundary treaties, which settled boundary disputes between the USA and Canada. As a leader of those Conservatives who campaigned for free trade, he supported Sir Robert Peel in repealing the Corn Laws (1846). As Prime Minister (1852–55) of the ‘Aberdeen Coalition’, he reluctantly involved his country in the Crimean War and was subsequently blamed for its mismanagement. He resigned in 1855.