John Temple Leader (7 May 1810 – 1 March 1903) was an English politician and connoisseur.
Born at his father's house, Putney Hill Villa, on 7 May 1810, he was the younger son of William Leader, a London merchant, and Whig Member of Parliament for Camelford and then Winchelsea. He entered Charterhouse School in 1823, but left shortly to study with a private tutor, the Rev. Patrick Smyth, and visited Ireland, Norway, and France. The accidental death at Oxford of his older brother William in February 1826 made him heir to most of his father's large fortune, which he inherited on his father's death on 13 January 1828.
On 12 February 1828 Leader matriculated as a gentleman commoner at Christ Church, Oxford, meeting there James Robert Hope Scott, W. E. Gladstone, and Sir Stephen Glynne with whom he made archæological excursions. In his Oxford vacations he continued his travels, and was in Paris daring the July Revolution of 1830; and there, through his father's friend Henry Brougham, he came to know leading liberal politicians. He took no degree, and after leaving Oxford went into politics.
Leader attached himself to the advanced wing of the Radicals, and was elected Member of Parliament for Bridgwater in January 1835. In the House he generally acted with George Grote and William Molesworth of the Philosophical Radicals, and supported the People's Charter of 1838. In his first session he seconded Grote's resolution in favour of the secret ballot. John Arthur Roebuck found him a useful politician, if also frivolous. Other party friends complained that his political speeches were too bitter.