Deciding on an architectural career while he was still in his teens Malcomson began training in the office of the late Mortimor L. Smith, and as draftsman remained in the latter's employ until 1885, when he started practice for himself. One of his earliest works was the Young Woman’s Home which still functions as such at Adams and Clifford Avenues in Detroit. In 1890 he entered into partnership with William E. Higginbotham, and for thirty-three years continued that association, the firm known to have designed more than three-quarters of the school buildings in the city. After completing in 1894 their first commission for the Central High School, now Wayne University they planned, successively, the Western High School, the Eastern, Southeastern! Southwestern, Northwsetern and Northern High Schools, Cass Technical High, 1920, and in 1927 won a competition for the Roosevelt High School group, he also planned the Hudson and Buhl Memorial at Harper Hospital in 1913, and completed work on the Henry Ford Hospital the following year Subsequent to the death of Mr. Higginbotham in 1923, Mr. Malcomson carried on work under his own name for a time. Between 1927 and 1934 he was associated in partnership with Alexander L. Trout, finally in August of 1937 (only a few months prior to his death) formed an architectural corporation with Ralph R. Calder, Maurice E. Hammond and Henry A. Fowler, men who had been associated with him for many years.
During the last decade of his practice Mr. Malcomson was identified with several educational buildings, including a group at the University of Detroit, won in a competition in 1924, Mosher-Jordan Halls at the University of Michigan, 1928, and at the Michigan State College at East Lansing, Chemistry Building, 1926; Mary Mayo Hall, 1928, and the Sarah L. Williams Hall, 1937. Other late works of his firm were the Municipal Building at Benton Harbor, Mich., and the King's Daughters and Sons’ Home for the Aged, Detroit, 1937.
Mr. Malcomson was prominently known in Detroit during his long and active career, member of the local Chapter of the A. I. A. after 1921, and in 1926 advanced to Institute Fellowship. He was also a member and past-president of the Michigan State Society of Architects. In 1937 he was honored by Wayne University with the degree of Master of Science in Architecture.