Van Leijenhorst attended a Gymnasium in Amersfoort from May 1940 until June 1946, and applied at the Utrecht University in July 1948 majoring in Physics and Chemistry obtaining a Bachelor of Science degree in June 1950 and worked as a student researcher before graduating with a Master of Science degree in Chemistry in July 1954. Van Leijenhorst worked as a chemistry teacher in Almelo from July 1954 until August 1955 and in Gouda from August 1955 until August 1971. Van Leijenhorst also worked as an education administrator for several Protestant educational organisations from March 1966 until August 1971. Van Leijenhorst served on the Municipal Council of Gouda from 1 September 1970 until 1 September 1971.
Van Leijenhorst was known for his abilities as a manager and policy wonk. Van Leijenhorst continued to comment on political affairs until his retirement in 1998, he died 3 years later at the age of 73.