Trumbull was born in what is now Watertown, Connecticut, where his father was a Congregational preacher. At the age of seven he passed his entrance examinations at Yale, but did not enter until 1763; he graduated in 1767, studied law there, and in 1771—1773 was a tutor. In 1773 he was admitted to the bar, in 1773—1774 practiced law in Boston, working in the law office of John Adams, and after 1774 practiced in New Haven, Connecticut. He was state attorney in 1789, a member of the Connecticut Assembly in 1792 and 1800, and a judge of the Superior Court in 1801—1819. The last six years of his life were spent in Detroit, Michigan, where he died.

While studying at Yale he had contributed in 1769—1770 ten essays, called "The Meddler", imitating The Spectator, to the Boston Chronicle, and in 1770 similar essays, signed " The Correspondent" to the Connecticut Journal and New Haven Post Boy. While a tutor he wrote his first satire in verse, The Progress of Dulness (1772—1773), an attack in three poems on educational methods of his time. His great poem, which ranks him with Philip Freneau and Francis Hopkinson as an American political satirist of the period of the War of Independence, was M'Fingal, of which the first canto, "The Town-Meeting", appeared in 1776 (dated 1775). After the war Trumbull was a rigid Federalist, and with the "Hartford Wits" David Humphreys, Joel Barlow and Lemuel Hopkins, wrote the Anarchiad, a poem directed against the enemies of a firm central government.