After commissioning, Stewart served for a short time at the Naval Academy and then joined the Coast Squadron of the North Atlantic Fleet.

On 17 April, as Stewart entered Quiberon Bay, an American steamer, Florence H, with a cargo of powder and steel, exploded in the anchorage.

She was forced to turn away at the last moment due to the effort of a French escort to ram the sub, but dropped two depth charges which brought up large amounts of oil.

The action was evaluated at the time as a kill; but the submarine, U-108, survived to be damaged by Porter several days later and finally to surrender at Harwich at the end of the war.

Decommissioned on 9 July, Stewart was struck from the Naval Vessel Register on 15 September, and sold on 3 January 1920 to Henry A. Hitner's Sons Company, Philadelphia, for scrap.