Downes conducted her shakedown off New York and in Chesapeake Bay and then returned to Philadelphia Navy Yard where she was placed in ordinary from 4 October 1915 to 26 May 1917 for the construction and installation of new machinery by the contractor. Fitted out for distant service, she sailed from New York on 18 October 1917 for Devonport, England, arriving 7 November.
From 17 November 1917 to 5 December 1918, Downes was based at Queenstown, Ireland and operated on convoy escort duty inbound to British ports, across the channel, and outbound to rendezvous with the ocean escorts. She patrolled against submarines off the Irish coast, making numerous attacks with no sure results and with other destroyers aided distressed ships. On two occasions her efficiency won commendations from the British Admiralty, once for her protection of the torpedoed Manley (Destroyer No. 74) and again for the rescue and salvage of a British submarine.
Downes arrived at Brest, France on 6 December 1918 to meet and escort President Wilson embarked in George Washington, passing in review before returning to Queenstown on 14 December. The day after Christmas, she sailed for the United States, arriving at Norfolk on 18 January 1919. After winter maneuvers in Cuban waters, she returned to New York on 14 March.
Downes reported to Norfolk on 5 May 1919 for overhaul and on 31 May was placed in ordinary. Returned to full commission, she sailed for Newport, Rhode Island on 12 May 1921 for summer maneuvers. Between 22 October and 20 March 1922, she lay at Charleston, South Carolina and on 24 March arrived at Philadelphia Navy Yard. She was placed out of commission there on 6 June 1922 and laid up.
Downes was transferred to the Coast Guard on 28 April 1924. Returned to naval custody at Philadelphia on 22 May 1931, she sold for scrapping on 22 August 1934 in accordance with the London Treaty for the reduction and limitation of naval armament.