He was born in Lebanon, Connecticut, the son of Joseph Trumbull (1678-1755) and his wife née Hannah Higley. He graduated from Harvard College with a B.A. in 1727; three years after graduation (during which time he studied theology under the Rev. Solomon Williams at Lebanon, and was licensed to preach at Colchester, Connecticut), this became a Master of Arts degree. He became a merchant with his father in 1731, participating more fully in the business after the death of his brother at sea in 1732. From 1733-1740 he was a delegate to the general assembly, and in 1739-40 was Speaker of the House. He was appointed lieutenant colonel in Connecticut's militia in 1739.
He served as deputy-governor of the Colony of Connecticut from 1766-1769, and on the death of the governor became Governor of Connecticut in 1769, serving in that capacity until 1784.
He was a friend and advisor of General Washington throughout the revolutionary period, dedicating the resources of Connecticut to the fight for independence. He was the only colonial governor to continue in office through the American revolution.
He received an honorary LL.D. from Yale University in 1775 and from the University of Edinburgh in 1787; Trumbull College at Yale is named for him.
He married, on December 9, 1735 Faith Robinson (1718-1780), daughter of Rev. John Robinson. They were the parents of six children including: