In 1894, Macomber joined the banking firm of N. W. Harris & Co as a messenger. In 1909, he became a partner, and he was named vice president in 1911. In 1916, the firm was succeeded by Harris, Forbes & Co. and Macomber was made president.[3] In 1930, he became chairman of the board of directors.[4] In 1931, the business was consolidated with Chase Securities to become Chase, Harris, Forbes Corporation.[5] In 1934, Chase, Harris, Forbes dissolved its banking affiliates and Macomber became chairman of the First Boston Corporation.[3] He retired from the board on December 31, 1947.[6]
During World War I, Macomber served as chairman of the New England Liberty Loan committee and of Metropolitan Boston trade in the United War Work campaign.[10][11] From 1919 to 1920, Macomber served as President of the Boston Chamber of Commerce.[10][12] On September 3, 1920, Massachusetts State TreasurerFred J. Burrell resigned following an investigation by a special legislative committee and Governor Calvin Coolidge appointed Macomber, Albert P. Langtry, and Henry A. Wyman to administer the office until a successor could be confirmed.[13] In 1922, Macomber was elected a life member of the board of trustees at Tufts College.[2] In 1926, he was named chairman of Massachusetts General Hospital's finance campaign committee.[14]
Macomber was the first president of the Eastern Horse Club, which conducted races at The Country Club and Raceland from 1926 to 1935.[3] After parimutuel betting was legalized in Massachusetts, Macomber, Charles Adams, Bayard Tuckerman Jr., and members of the Eastern Horse Club formed the Eastern Racing Association to open a thoroughbred race track in East Boston.[20][21] At Macomber's suggestion, the new track was named Suffolk Downs.[3] Beginning in 1956, the closing race of Suffolk Downs' spring meeting was called the John R. Macomber Memorial Handicap.[3]
Steeplechase
In 1928, Macomber's horse Bridge won the inaugural Master of Foxhounds Association Steeplechase for hunters in front of a crowd of 10,000 at Pimlico Race Course.[22] In 1929, his horse Coronel won The Country Club Grand National steeplechase race.[23]
Macomber was a lifelong resident of Framingham. He lived with his mother in the family home for 50 years. After her death, he developed Raceland, which served as his home as well as a venue for horse racing, dog shows, and automobile shows. Beginning in 1927, Macomber opened Raceland to the public free of charge for one day of the annual horse meet.[24] In 1930, the stable and clubhouse were destroyed by fire, but he replaced the buildings in time for the next year's meet.[25]