Henry John Temple, third Viscount Palmerston, entered Parliament in 1807 and served as secretary at war from 1809 to 1828. The long tenure gave him extensive administrative experience during the Napoleonic Wars and their aftermath. Initially associated with Tory governments, he later moved toward the Whigs. As foreign secretary in 1830–1834, 1835–1841, and 1846–1851, he became identified with an assertive defense of British interests abroad.

Palmerston supported recognition of Belgian independence while seeking a European settlement that prevented French domination of the new state. In the eastern Mediterranean he resisted Muhammad Ali's expansion from Egypt, participating in the 1840 intervention that preserved the Ottoman Empire. His foreign policy combined support for constitutional movements with strategic calculation and the protection of trade.

His tenure included the First Opium War against China, a conflict tied to commercial interests and the opium trade. In the Don Pacifico dispute of 1850, he ordered coercive action against Greece in support of a British subject's compensation claim. Critics argued that such methods endangered peace and treated weaker states unfairly. Queen Victoria and other ministers also objected to his tendency to act without adequate consultation.

Dismissed as foreign secretary in 1851 after approving Louis Napoleon's coup without prior cabinet agreement, Palmerston soon returned to office as home secretary. In 1855, during the Crimean War, he became prime minister after the collapse of Lord Aberdeen's coalition. His government continued the war and helped conclude the peace of 1856. A parliamentary rebuke over the bombardment of Canton led him to seek an election in 1857, which produced a substantial victory; another controversy involving the attempted assassination of Napoleon III brought his first ministry down in 1858.

Returning as prime minister in 1859, Palmerston remained in office until his death in 1865. He favored stronger defenses, resisted extensive parliamentary reform, and maintained British neutrality during the American Civil War despite pressure for intervention. Popular for his confident public manner and nationalism, he helped make foreign policy a subject of mass political attention. His career joined administrative longevity and parliamentary skill to an imperial diplomacy whose use of force remains central to assessing his reputation.