William Francis Cowper-Temple, 1st Baron Mount Temple (December 13, 1811) - (October 16, 1888) was a British Liberal politician and statesman. The son of the 5th Earl Cowper , he was also a nephew of Prime Minister Lord Melbourne, and eventually became stepson to another Prime Minister, Lord Palmerston. He was born at Brocket Hall, Hertfordshire, and educated at Eton. After entering the Royal Horse Guards in 1830, he was promoted Captain five years later, eventually attainig the rank of Major in 1852.

In 1835, Cowper was elected Liberal Member of Parliament for Hertford, a seat he held for the next thirty-five years, and became private secretary to his uncle as Prime Minister. He was appointed a Groom in Waiting in 1837, and in 1841 served for three months as a Lord of the Treasury, only resuming office five years later as a Lord of the Admiralty when the Whigs returned to power. He again held this post from 1852 to 1855, and in the latter year was made Under Home Secretary by his stepfather when he became Prime Minister. In August that same year he was appointed President of the Board of Health, and four years later became Paymaster General, only serving for a year before his stepfather made him Chief Commissioner of Works.

In 1866, on the fall of Lord Russell's government, Cowper left office for good. Two years later he was returned to Parliament for South Hampshire, and held this seat until his ennoblement in 1880 as Baron Mount Temple, of Mount Temple in the County of Sligo. His mother having died in 1869, he inherited a number of estates under his stepfather's will, and so took that year under royal licence the additional surname of Temple.

Lord Mount-Temple died aged 76 at his home of Broadlands, Hampshire, and was buried at nearby Romsey. He left no children at his death, and so his peerage became extinct.