Sir Thomas Hewet or Hewett (9 September 1656 – 9 April 1726) was an English landowner and architect.
He was born the son of William Hewet of Shireoaks Hall, Nottinghamshire and educated at Shrewsbury School and Christ Church, Oxford. matriculating in 1676. He then spent several years travelling the continent of Europe. He inherited his father's estate, including Shireoaks, as a child in 1660 and eventually took possession in 1689.
He became an architect and won some valuable clients. He built a library in Piccadilly for Charles Spencer, 3rd Earl of Sunderland and advised Thomas Parker, 1st Earl of Macclesfield on the restoration of Shirburn Castle, Oxfordshire. Sunderland recommended him in 1719 for the position of Surveyor of the King's Works based at the Tower of London. He had also been appointed Surveyor-General of Woods in 1701 and 1714. He was knighted in 1719 and elected a Fellow of the Royal Society in 1721.
At his family seat, Shireoaks Hall, he carried out major renovations and improvements, remodelling the front, adding a wing and creating avenues and a water garden. The work was not entirely complete at his death but he willed funds for its completion.
He died in 1726 and was buried in the local church at Wales, Yorkshire. He had married Frances Betenson, the daughter of Richard Betenson in 1689 in Geneva. It is said that Sir Thomas left his estate to his godson John Thornhaugh of Osberton because their only daughter had run off with a fortune-teller.