Born in Scotland, Robert B. Williamson immigrated to America with his family in 1869 as a child. His father, Robert B. Williamson Sr., was a cabinetmaker in Chicago. R. B. Williamson and his brother William G. Williamson both became architects, although Robert’s brother William achieved a higher degree of prominence than he. They were both members of the Chicago Sketch Club which later became known as the Chicago Architectural Club. According to Wilbert R. Hasbrouck, author of The Chicago Architectural Club: Prelude to the Modern, both brothers participated in one of the club’s early competitions in 1885. William G. Williamson received second place and Robert B. Williamson placed third in this competition in which draftsmen and architects submitted detailed sketches and renderings.
In 1902, Robert B. Williamson was listed as one of seven superintendents of construction in the architect’s department of the Board of Education. In May of 1904, soon after William B. Mundie’s resignation, the Board of Education appointed Williamson as acting architect. Williamson remained in the position for one year. In 1905, the board instituted a new policy by which candidates for head architect were required to take a civil service examination. Williamson took the exam, but was not among the highest scoring candidates. According to a Chicago Tribune article, when Dwight H. Perkins received the highest score on the exam and was under consideration for the position in June of 1905, Williamson asserted that Perkins was ineligible for the position because he was not a legal resident of Chicago. A hearing determined that Perkins did have an appropriate Chicago address. Perkins was appointed to the position of head architect, and Williamson was reinstated as a superintendent of construction. In this arrangement, Williamson served under Perkins’s leadership.
During Williamson’s short tenure as acting architect he was credited with designing an addition to Nixon School and producing plans for Graham School. By the 1920s, Robert B. Williamson was practicing architecture on his own and according to the American Contractor, in 1922, he was considered the successor to his brother William G. Williamson’s firm.