After serving in the Swedish army as a topographical surveyor, Ericsson went to London in 1826 and constructed a steam locomotive, the Novelty, for a railway competition at Rainhill, Lancashire, in 1829. The prize was won by George Stephenson (Stephenson, George)'s Rocket. Ericsson also devised a plan for placing warship engines below the waterline to protect them against shell fire. In 1833 he exhibited his caloric engine, on which he worked the rest of his life, and in 1836 he patented a screw propeller, first used in 1837 on the Francis B. Ogden, built in London. Captain Robert F. Stockton (Stockton, Robert F.), of the U.S. Navy, ordered a small iron vessel, the Robert F. Stockton, to be fitted by Ericsson with engines and screw; it reached New York City in May 1839.

A few months later, Ericsson emigrated to the United States and lived the rest of his life in New York City, becoming a naturalized citizen in 1848. During the American Civil War, Ericsson's proposal to the Navy Department for a novel warship was accepted, and the Monitor was launched on January 30, 1862. Wholly steam-powered and with a screw propeller, the vessel, with its armoured revolving turret, set a revolutionary pattern for warships that continued into the 20th century. On March 9 the Monitor fought the Confederate ironclad Virginia (formerly Merrimack), leading the federal government to place an order with Ericsson for many more Monitor-type vessels; these ships played an important role in the blockade of the Confederacy. (See Battle of Monitor and Merrimack (Monitor and Merrimack, Battle of the).) In later years he developed a torpedo and investigated solar-powered motors.