As a child Fitch had few years of schooling and suffered from a harsh father. He apprenticed himself to a clock maker, learned brass working, and later opened his own brass foundry. However, due to inefficient business practices he was unsuccessful in both this endeavor and as a silversmith. He did make some money managing a gun factory during the Revolutionary War, but the colonial currency became worthless, and he passed the last part of the war as a British prisoner.

Settling in Pennsylvania after the war, Fitch concentrated on inventing a steam-powered boat. Using a working model, he was granted a fourteen-year monopoly from five state governments to operate his craft on their waters and secured the backing of a group of Philadelphia investors. On August 22, 1787, he successfully demonstrated a 45-foot (13.7 m) boat on the Delaware River before delegates to the Constitutional Convention. This craft was propelled by six paddles on a side like an Indian canoe but was driven by a steam engine . The next year he built a 60-foot (18 m) paddle wheeler with paddles that moved like ducks' feet, and in 1790 an even larger boat was launched, one which for a time maintained a regular schedule of trips between Philadelphia and Trenton. However, the number of passengers, never great in the first place, dwindled, making the route a money loser. His backers then quit, and a fourth boat was wrecked in a storm in 1792.

Fitch later attempted to spread his ideas in Europe. He secured a French patent in 1795, but the French Revolution prevented him from continuing business in that country. The project failed, and he had to return home as a seaman to pay for his passage. Although in poor health, Fitch continued to pursue backers but to no avail. He died in 1798, nine years before Robert Fulton repeated his work and received credit for the invention of the steamboat.