Thistlewood began his Caribbean life as an overseer, first at Vineyard Pen, a cattle pen that provided meat and vegetable provisions to sugar plantations. He then worked primarily at Egypt, a sugar plantation owned by John Cope and William Dorrill, where he was an overseer from 1751 to 1767. The plantation was in Westmoreland Parish, where he supervised numerous slaves in sugar production. Egypt comprised 1,500 acres of land, of which 1,200 consisted of water and morass and were thus unsuitable for sugar production. Only 150 acres were in cane, and Thistlewood's first crop was so poor that Dorrill considered switching Egypt from sugar to a cattle pen.