Carver was promoted to lieutenant (1759) and then to captain (1760) while serving in a Massachusetts regiment during the French and Indian War. In 1766 he was sent by Major Robert Rogers (Rogers, Robert) on a journey of exploration westward from Rogers' base at Fort Michilimackinac (now Mackinac, Mich.). Carver traveled west through the Great Lakes region to the Mississippi River and then up that river to the country of the Sioux Indians. Alone, he spent the winter of 1766–67 at a Sioux village on the Minnesota River. Returning to Fort Michilimackinac in the spring, he met Captain James Tute in command of a party that had been sent out by Rogers to explore a route to the Pacific Ocean. Tute brought orders for Carver to join the party as draftsman and third in command. They proceeded up the Mississippi and skirted the shores of Lake Superior to the Grand Portage. Failing to receive supplies, the party abandoned the expedition and returned to Fort Michilimackinac (August 1768).

Rogers had hired Carver without authorization, and as a result Carver was never paid for his services. Carver left for England in 1769 to have his journal published, but the project met with many delays. His journal was finally published in 1778 in London as Travels Through the Interior Parts of North America in the Years 1766, 1767, 1768; it was an immediate success and eventually went through more than 30 editions. The book gives a vivid picture of the rich lands and Indian inhabitants of the upper Mississippi River valley. Carver, however, did not live to enjoy any financial reward from it. He died a broken old man and was buried in a potter's field.