He graduated from the Keystone State Normal School in 1870 and from Lafayette College in Easton, Pennsylvania, in 1874 and was a member of Chi Phi fraternity.

He studied law under John D. Stiles, was admitted to the bar in 1877 and commenced practice at Allentown, Pennsylvania, in 1878.

In 1906, he led the investigation of the Pennsylvania State Capitol Graft Scandal.

He served as adjutant of the Fourth Regiment of the Pennsylvania National Guard for ten years.

Dewalt was elected as a Democrat to the Sixty-fourth, Sixty-fifth, and Sixty-sixth Congresses.