He was in the Judge Advocate General's Corps of the United States Army Reserve from 1960 to 1968 and in private practice in San Antonio from 1963 to 1965.

He was from 1965 to 1966 a legal counsel for the United States Senate Committee on Labor and Public Welfare in Washington, D.C.[1] Nowlin was a Democratic member of the Texas House of Representatives from 1967 to 1971 and a Republican from 1973 to 1981.

[3] Rather than seeking a third consecutive term in the House, Nowlin ran unsuccessfully as a Republican in 1970 for the Texas State Senate.

[2] Nowlin returned to the private practice of law in San Antonio in 1966 and remained so engaged until 1981.

On September 17, 1981, President Ronald Reagan nominated Nowlin to a seat vacated by Judge Jack Roberts.