In the early years of Missouri's statehood, there was no centralized path to becoming an attorney, nor was there any broad organization of attorneys. Largely, those aspiring to become attorneys apprenticed with those already practicing law and then were endorsed to begin practicing themselves.

As the state's population – and, with it, the number of lawyers – grew, attorneys began to form local associations. One of these, for example, exerted influence in the 1870s to successfully urge state constitutional convention delegates to create an intermediate court of appeals in St. Louis to alleviate the burden of appeals from the area on the Supreme Court of Missouri. But there still existed no statewide association of attorneys.

Then, in December 1880, a group of 107 lawyers assembled in Kansas City to form an organization they called the Missouri Bar Association. Approximately five decades later, they amended their constitution to welcome local bar associations to become affiliate members, increasing cooperation among like-minded groups to carry out policies, plans and adopted measures. Shortly thereafter, the Missouri Bar Association members expressed a desire to have a self-governing bar in Missouri, in which every lawyer practicing in the state "would be an active part and parcel." A joint commission was formed to make recommendations to the Supreme Court of Missouri. 

In response to the joint commission's recommendations, the Court adopted a new rule – effective in November 1934 –establishing canons of ethics for lawyers, creating circuit bar committees to investigate ethics complaints, and requiring the paid enrollment of all practicing attorneys to support an advisory committee and Missouri Bar administration. By 1942, the state association's members agreed "to devise a plan for complete self-government of the Missouri Bar Association to assure all the benefits of unity and action by all Missouri lawyers."

The following year, in October 1943, hundreds of lawyers assembled in Kansas City for the 63rd annual meeting of the Missouri Bar Association to discuss a resolution paving the way for a wholly integrated bar. During the meeting, at which "the seats were filled," bar leaders described the need for "an all-inclusive, self-governing state Bar" to "marshal the man power of the whole Bar of Missouri into one organization … [to] be much more effective in the work that we are trying to do," with others desiring urgency to achieve unification to ensure the younger lawyers, many of whom were serving their nation during World War II, would return to "a worthwhile up-to-date" bar association and "a system of judicial procedure, a system of court organization which is superior to anything they have known heretofore."

After the unanimous vote of the assembly, and the favorable vote of a committee appointed to inquire into integration of the bar, the Supreme Court of Missouri on June 16, 1944, adopted a rule unifying and integrating all the state’s lawyers into a new organization called, simply, The Missouri Bar.

In June 2019, then Chief Justice Zel M. Fischer – on behalf of the entire Supreme Court of Missouri – recognized the Bar for the faithful manner in which it has served Missouri's citizens, lawyers and nonlawyers alike and gratefully acknowledged the Bar's significant contributions to the administration of justice and legal profession in Missouri.