Splawn taught at his alma mater from 1910 to 1912, then began the practice of law in Fort Worth, Texas.

[4] After leaving Austin in 1928, Splawn served as dean of the graduate school of American University, in Washington, D.C., between 1929 and 1934.

[3][4] Splawn served on the federal War Claims Commission as referee in 1927, and concurrently led the Board of Arbitration of Western Railroads and Group of Employees as chairman.

In the 1930s, Splawn served as counsel to the United States House of Representatives' Committee on Interstate and Foreign Commerce.

Splawn grew close to representative Sam Rayburn, and was subsequently appointed to the Interstate Commerce Commission between 1934 and 1953.