Bob Larmore was born in Anderson, Indiana on December 6, 1896 to parents James, and Maude Larmore of Ohio, and Indiana, respectively. Fred G. Larmore owned and operated Larmore Ice Cream Company, which was incorporated in 1918. Bob Larmore attended Central High School in St. Louis Missouri. In May 1918, while still in high school, Larmore was signed by the Major League Baseball St. Louis Cardinals. Before signing with Cardinals' managerBranch Rickey, Larmore informed him that he wished to continue attending school. He was the first player in the history of Major League Baseball to be playing for a team while still attending high school. Larmore's teachers at school allowed him to leave at noon every day to go to Cardinal Field. He was intended to be the fill-in at shortstop for St. Louis, who were absent a player at that position due to an injury to Rogers Hornsby. Larmore made his MLB debut as a pinch runner on May 14, 1918, in a game against the Philadelphia Phillies. His first MLB hit came on May 18, in a game against the Boston Braves. On June 22, Larmore made his final MLB appearance. On the season with the Cardinals, he batted.286 with two hits, and one run batted in in four games played. Larmore was farmed out to the minor league Houston Buffaloes of the Class BTexas League in late-June. With the Houston club, he batted.238 with five hits in eight games. In July, the Texas League suspended its operations due to World War I. That month, Larmore was re-called to the major leagues. However, he never made an appearance. In August, he enlisted into the United States Navy to fight in World War I.
At the start of the 1919 season, the St. Louis Cardinals sold Larmore to the minor league Houston Buffaloes. He reported to spring training with Houston in April 1919. On June 18, he was traded to the Dallas Marines, also of the Texas League, in exchange for Billy Patterson. Between the two clubs, he batted.240 with 124 hits, 20 doubles, seven triples, and three home runs in 110 games played. His last professional baseball season came in 1920. At the start of the season, Larmore played with the Cedar Rapids Rabbits of the Class-B Illinois–Indiana–Iowa League. With the Rabbits, he batted.266 with 111 hits, 12 doubles, 10 triples, and four home runs in 111 games played. Larmore then joined the Joplin Miners of the Class AWestern League. He batted.194 with 14 hits, one double, and one triple in 22 games played. After his career was over, Larmore enrolled at University of Missouri, and pledged Beta Theta Pi. By 1930, he was working as a salesman for his brother's ice cream company. He resided in St. Louis, Missouri with his wife Mary, and their child, Constance. Larmore died on January 15, 1964 in St. Louis. He was buried at Oak Grove Cemetery in St. Louis.