Sir George Downing, 3rd Baronet, KB (baptized 24 October 1685 – 10 June 1749) was a politician and, through a donation in his will, the founder of Downing College, Cambridge.
He was only son of Sir George Downing, 2nd Baronet, and his wife, Lady Catherine Cecil, daughter of James Cecil, 3rd Earl of Salisbury. His mother died in 1688, and, with his father considered an unsuitable parent, he was brought up in the family of his maternal aunt, the wife of Sir William Forester of Dothill Park, in Wellington, Shropshire. In 1700, aged 15, 'by procurement and persuasion of those in whose keeping he was', he married his 13-year-old cousin, Sir William's daughter, Mary, who ultimately died childless in 1734. Between his marriage and 1704 he travelled in Europe, mainly Holland, Germany, Denmark and Italy.
He was a Member of Parliament for the pocket borough of Dunwich, Suffolk in the parliaments of 1710 and 1713. He lost the 1715 election but, with the aid of a 99-year lease from George I for the borough, regained the seat in 1722. He held the seat from that time until his death. He was an uninspiring politician, but remained loyal to the ministries of Robert Walpole and subsequently Henry Pelham. In 1732, as a result of his loyalty, he was created a Knight Companion of the Order of the Bath.
Downing succeeded to his father's baronetcy and estates in 1711. He built a grand family seat in Gamlingay Park in Cambridgeshire. Upon his own death, aged 63, in 1749, his title passed to his cousin, Sir Jacob Downing, 4th Baronet, with his will providing that if his line should die out, his fortune should be used to found a college at Cambridge University. Sir Jacob Downing died childless in 1764, but his widow, Lady Downing, argued that Downing's fortune should pass to her. This case was tied up in litigation for decades before the courts finally ordered that the fortune should be used to found a college at Cambridge, which occurred with the founding of Downing College, Cambridge in 1800.