He was born in New York City to parents Graham Livingston Montgomery and Anne Cook and lived in Greenwich Village until 1930, when he moved to Port Washington, Long Island. Roger's father died suddenly from a heart attack in 1942. In 1945 he was accepted into the army, where he served in an intelligence unit in occupied Germany as a radio operator. On April 23, 1949 Roger married Oberlin College graduate Mary Hoyt. Roger has four sons, Richard Wallace (born 1956), Thomas Vinton (1958), John 1960, and Peter George (1965). In 1957 Roger was diagnosed with multiple sclerosis. He died of cancer on October 25, 2003.
Roger attended a John Dewey-influenced grade school in Port Washington, which emphasized mechanical skills over traditional subjects such as reading and writing. In high school he was voted ‘Most Likely to Succeed’ and ‘The Great Orator’. He was excused from military service in 1941 because of a punctured eardrum and subsequently enrolled in Oberlin College, but was dismissed from the college in 1945. Roger began his architectural work in 1948 as an apprentice in Springfield, Ohio and was soon successful, in part because of a shortage of architects and large post-war boom in construction. From 1955 to 1956 Roger attended the Harvard Graduate School of Design where he received a Masters of Architecture degree under professors Josep Lluís Sert and Sigfried Giedion, while studying with classmates Fumihiko Maki and Ben Weese.
1960: Started the architectural practice of Schnebli, Anselevicius, and Montgomery (SAM) that designed the Washington University Law School Building in 1972. Founded the Urban Design Program at Washington University with Fumihiko Maki
1961: Worked for the Kennedy Administration as the first Urban Design Officer in the Federal Housing and Home Finance Agency (later HUD).
1980s: During this period Montgomery served as President of the California Council of Architectural Education, and the National Board of Architects, Designers and Planners for Social Responsibility. Additionally, he served on boards for a number of voluntary organizations related to the design professions including Planners for Equal Opportunity, Planners Network and Northern California Non-Profit Housing Coalition. In the Bay Area, Montgomery advised City and County boards in Berkeley, Alameda County, Santa Clara and San Francisco. Montgomery was also named Associate Dean for Undergraduate Affairs and later Acting Dean.