Subsequently, Carlsen taught and coached at North English High School for two years.
Upon completing his studies at the University of Iowa College of Law in 1937, Carlsen began practicing law alongside the continuation of his teaching and coaching career at Clinton High School.
Carlsen coached high school football, wrestling and track until 1941, when he began working for the Federal Bureau of Investigation.
Between 1955 and 1959, Carlsen occupied the District 45 seat in the Iowa House of Representatives as a Democrat.
After stepping down from the state legislature, Carlsen became assistant county attorney, and was appointed to an alternate municipal court judgeship during the Harold Hughes and Robert D. Ray gubernatorial administrations.