Fellenz was a member of the Senate representing the 18th district from 1941 to 1948. He was a Republican.[2][3] He attempted several times to join the armed forces during World War II, and after passing a physical for the United States Army in May 1944, he resigned from the state Senate and enlisted.[4] He was elected to another term as state senator without opposition during his brief stint in the Army, and was discharged in December 1944.[5]
Louis Fellenz Jr. was one of three children born to L. J. Fellenz and his wife Erma Emma (née Tabor). Louis Sr. was also a lawyer and state senator, and served as a Wisconsin circuit court judge for the last 10 years of his life.[7][8]
On June 1, 1941, Louis Jr. married Virginia Skinner at her parents' summer home in Green Lake, Wisconsin.[7] They had two children together and were married for nearly 52 years before his death in 1993.[6]