From 1941 to 1945, McGrath was Governor of Rhode Island, reorganizing the juvenile court system while sponsoring a workers' compensation fund and a labor relations board, but he resigned in the middle of his third term to accept appointment as Solicitor General of the United States (1945–1946).

[3] ... convention convened at the Rhode Island College of Education auditorium in Providence, March 28, 1944 for the purpose of amending the State constitution to eliminate voting registration requirements by members of the armed forces, merchant marines or persons absent from the state performing services connecting with military operations.

Delegate continent totaled 200 with Governor J. Howard McGrath serving as president & William A. Needham of Providence as Secretary.

In the Senate, McGrath opposed reducing wartime economic controls and taxes, wishing to spend the latter instead on Social Security, national health insurance, and education.

In managing President Harry Truman's successful 1948 election campaign, McGrath alienated white Southerners but won over crucial black constituencies by integrating the Democratic national headquarters staff.

[5][6] Alternative accounts have contradictorily suggested that after a meeting of the Joint Chiefs of Staff at Truman's "Little White House" in Key West, the Secretary of the Navy, along with other members, had threatened to resign if they, too, were forced to comply with Special Assistant Attorney General Newbold Morris's request for the personal records of all members who might have received gifts under the scope of the corruption investigation.