Robert Rienow was born in Grafton, Wisconsin on December 4, 1907, and later in life married Leona Train, a writer of children's books and articles, and his occasional co-author. After a year at West Point, Rienow continued his education at Carthage College in Kenosha, Wisconsin, receiving a Bachelor of Arts degree in history in 1930. His first job was as a school principal at a small school in Wisconsin. Rienow went on to earn advanced degrees from Columbia University in the field of international law and government (M.A., 1933; Ph.D., 1937). While obtaining his master's degree, he taught for one year at Union College in Schenectady, New York. Rienow was also the recipient of Columbia University's Gilder Fellowship in Public Law. In 1935, Rienow attended Ohio State University as part of a research fellowship. ["Rienow to Discuss National Doctrine, Re-sing Scheduled", Unidentified News Clipping, 5 December 1947]. His Ph.D. dissertation was titled "The Test of the Nationality of a Merchant Vessel". While Rienow was completing his Ph.D. at Columbia he served as an Instructor of Political Science in the Social Sciences Department at the New York State College for Teachers, which later became the State University of New York at Albany and is presently known as the University at Albany, SUNY. Rienow continued in this position until 1941, when he was promoted to the position of Assistant Professor. Rienow was promoted to Professor in 1947 and held this position until 1980.

In July of 1943, Rienow took a leave of absence from his teaching position to serve in the United States Army during World War II. Rienow held a Selective Service position as a Classification Specialist, both in the United States and in the Pacific Theater, until 1945, when he was honorably discharged. He ended his career with the United States Army in 1946 at the rank of First Lieutenant in the Adjutant General's Office. Upon his return, Rienow served in the New York State National Guard in the Selective Service branch, rising to the rank of Lieutenant Colonel. In 1962, Rienow, along with his unit, received an award on behalf of the National Guard for the superior ratings received by the unit at regular army inspections.

Rienow was a prolific writer who published books and articles on both political science and environmental issues. The most prominent of these was Moment in the Sun (1967), which he co-authored with his wife. Other significant works were Calling All Citizens (1952), New York State and Local Government (1959), Introduction to Government (1964), Our New Life with the Atom (1959), Of Snuff, Sin, and the Senate (1965), and The Lonely Quest (1966). The final three were co-authored by Rienow and Leona Train Rienow. Rienow also wrote numerous articles, both alone and in collaboration with his wife. Most of these articles expressed concern about environmental issues, though some were humorous or satirical pieces. Rienow's articles were published in magazines such as Harper's Weekly, This Week, the American Legion Magazine, the Saturday Review, and Ladies Home Journal.

Rienow maintained a vigorous interest in environmental issues throughout his life. A noted speaker, he delivered many lectures and presentations on environmental issues. In the late 1960s he developed a series of broadcasts on the environment in cooperation with the State University of New York at Albany's School of Public Policy. The series, Man Against His Environment, consisted of 28 lectures on topics such as water pollution, wildlife protection, overpopulation and zero population growth, as well as many others.

Rienow was a member of numerous environmental organizations, including Defenders of Wildlife, the Constitutional Council for Forest Preserves, the Audubon Society, the Sierra Club, and the Albany Environmental Council. He was an officer of the New York Chapter of The Nature Conservancy. Rienow's professional affiliations included the New York State Political Science Association, of which he was elected president in 1955. ["SCT President Heads Political Science Unit", Unidentified News Clipping, April 1955.]

Robert Rienow died in 1989 as the result of a fire in his home.