Walsh entered into private practice in Cumberland until 1916, when he joined the First Maryland Infantry.
He served in the campaign in Mexico against Pancho Villa, and in France during World War I.
[1] In September 1921, at the age of 31, he was appointed as an associate justice of the Maryland Fourth Judicial Circuit; he "was believed to be the youngest judge to ever sit on a circuit bench in the state".
[1] Walsh then served as State Insurance Commissioner from 1931 to 1935, and Attorney General of Maryland from 1938 to 1945, resigning to form the law firm of Tydings, Walsh, Levy & Archer with former Senator Millard Tydings.
He died in Cumberland, where he was interred, in Saints Peter and Paul Cemetery.