Thomas "Diamond" Pitt (5 July 1653 – 28 April 1726) of Stratford in Wiltshire and of Boconnoc in Cornwall, was an English merchant involved in trade with India who served as President of Madras and six times as a Member of Parliament.
He was the grandfather of William Pitt, 1st Earl of Chatham ("Pitt the Elder") and was great-grandfather of Pitt the Younger, both prime ministers of Great Britain.