In 1911, Truman lead the effort to organize Masonic Lodge 618 in Grandview. He was elected its first master, served as secretary for four or five years, and was elected master for a second time in 1916. The Masons became an important part of Truman's social life, and he gave himself energetically to learning Masonic ritual and participating in meetings and ceremonies at several lodges in Jackson County. The thrill of being a leader among his Masonic brothers was strongly felt by a young man who had struggled for years to get over his shyness. "I have the big head terribly," he wrote proudly to Bess Wallace when he was elected master in 1911. (Letter of June 16, 1911.) About a month after becoming master, he conferred the first degree that was given in the Grandview lodge. "…Some time in the far distant future," he wrote Bess, "I'll be bragging about having performed that ceremony." (Letter of July 29, 1911.) He was frequently asked to officiate at Masonic ceremonies. He wrote Bess in late February 1912 that he had to preside over ceremonies at three different lodges on three consecutive nights. "That dispenses with three nights on which I receive nothing but hot air and get my hatband sprung," he said. (Letter of February 27, 1912.)
While Truman was serving in France during World War I, the lodge hall in Grandview burned down and all its records were lost. After the war, Truman focused his efforts on serving the entire Masonic district that included Jackson County outside of Kansas City. In 1925, he was appointed District Deputy Grand Master and Lecturer and for about five years he gave courses of instruction in lodges throughout the district.
Gaylon Babcock, whose family owned a farm near the Truman farm in Grandview, attended lodge meetings with Truman in the 1920s. Babcock was very critical of Truman's ability as a farmer, but he thought better of the skills he demonstrated in his Masonic work. "…He did a good job in the lodge work. Excellent. He was an excellent director. If things weren't going right along smoothly, Harry would come in and get them to going. He was a good lodge man." (Gaylon Babcock oral history interview, Truman Library, 1964.)
In 1940, Truman was elected Grand Master for the Grand Lodge of Missouri. His last duty in this position was to preside over the lodge's annual meeting, held in St. Louis on September 30 and October 1, 1941. "Well my tour of duty as Grand Master ended up in a blaze of glory…," Truman wrote to Bess after the meeting. "My good friends were the happiest men you ever saw and I felt like it was worth all the effort and time." (Letter of October 3, 1941.)
On October 19, 1945, Truman was given the 33rd degree of the Supreme Council of the Scottish Rite for the southern jurisdiction. He is the only President to have received this distinction, which he considered with satisfaction to be the culmination of his Masonic career. "Freemasonry," Truman wrote in 1939, "is a system of morals which makes it easier to live with your fellow man, whether he understands it or not." (Letter to Frank P. Briggs, December 13, 1939. Papers as U. S. Senator and Vice President.)