John Dennistoun (19 March 1803 – 9 September 1870) was a British Whig politician and banker.
A member of Brooks's, he was elected Whig MP for Glasgow at a by-election in 1837—caused by the resignation of James Oswald—and held the seat until 1847 when he was defeated.
His wife Frances was the daughter of Sir Henry Onslow. His brother Alexander Dennistoun was Whig MP for Dunbartonshire from 1835 to 1837.