Jemison came from a family of prominent ministers; he was born in Selma, Alabama, where his father, the Rev. David V. Jemison, pastored the Tabernacle Baptist Church. At the time he moved to Baton Rouge to lead Mt. Zion First Baptist Church in 1949 , his father was serving as President of the National Baptist Convention.
Before his arrival in Baton Rouge Rev. Jemison had degrees from Alabama State University and Virginia Union University, and he had done graduate work at New York University. He began his service as a minister in Baton Rouge in 1949, concerned chiefly with internal church matters, such as the construction of a new church building.
A boycott of the Baton Rouge bus system by black citizens in 1953 was forerunner of the more famous Montgomery Bus Boycott of 1955-1956. Like many southern cities in the 1950s, Baton Rouge buses were segregated; black riders had to sit at the back of the bus or stand even if seats at the front were empty.
Jemison was struck by the sight of "buses heading into south Baton Rouge, filled with people standing behind rows of empty seats" . Those African-American passengers who rode the bus—and who made up 80% of the passengers on the system—were likewise fed up with standing while "white" seats remained empty, particularly after the company had raised fares from ten to fifteen cents in January, 1953.
Rev. Jemison took up the issue with the Baton Rouge City Council, going before it on February 11, 1953 to denounce the fare increase and ask for the end of the practice of reserving seats for whites. The City Council met that demand, without abolishing segregation per se, by passing an ordinance that allowed black passengers to board the bus from the back, taking any empty seats available, while white passengers boarded from the front. The bus companies, however, largely ignored the ordinance.
When bus drivers abused black passengers seeking to enforce the ordinance, Rev. Jemison tested the law on June 13, 1953 by sitting in a front seat of a bus. The next day the bus company suspended two bus drivers for not complying with the ordinance. The drivers' union responded by striking for four days. That strike ended on June 18, 1953 when Louisiana Attorney General Fred LeBlanc declared the ordinance unconstitutional on the ground that it violated the state's segregation laws.
In response, that same day blacks formed the United Defense League (UDL). Led by Jemison and Raymond Scott, the UDL was formed to organize a bus boycott in Baton Rouge and to bring suit against the City to desegregate the buses. The organization set up a free-ride network to compensate for the lack of public transit, a system that the organizers of the Montgomery bus boycott learned from when undertaking their year-long boycott two years later. As Dr. Martin Luther King, Jr. wrote, Jemison's "painstaking description of the Baton Rouge experience proved invaluable" .
The great majority of bus riders were black, and most of them refused to ride the buses. By the third day, the buses were almost entirely empty. A volunteer 'free ride' system was co-ordinated by the churches, and many others chose to walk to work. The boycott lasted only a week, as Rev. Jemison called off the boycott on June 23, 1953 after negotiations between black leaders and the city council. The following day the city council passed an ordinance under which the first-come, first-served, seating system of back to front and front to back was reinstated while setting aside the first two seats on any bus for white passengers and the back bench for black passengers and allowing anyone to sit on any of the rows in the middle. To comply with state segregation laws, blacks and white were prohibited from sitting next to each other, the two front sideways seats were absolutely reserved for whites, and the wide rear seat at the back of the bus was reserved for blacks.. While a number of boycotters wanted to attack segregation directly, the majority approved the compromise.
Others dispute Jemison's role in the boycott. Willis Reed, the publisher of the Baton Rouge Post, and a political activist within the black community in 1953, has stated that other organizations began organizing against segregation on the city's buses before Jemison took up the issue. Jemison himself acknowledges that the boycott was not an all-out assault on segregation, but only an effort to obtain fairer treatment for African-American bus riders. Yet the boycott established the model for Montgomery: a nonviolent mass movement, organized through the black church that confronted the white establishment both in courts and in the economic sphere.
Jemison's finest achievement of his tenure as President of the National Baptist Convention was the construction of the Baptist World Center in Nashville, Tennessee, which acts as a Headquarters for the Convention. He was also more prepared to speak out on issues of the day than his predecessor Joseph H. Jackson had been, notably opposing the Gulf War and the nomination of Judge Clarence Thomas to the United States Supreme Court. Towards the end of his term as President, Jemison faced difficulties caused by his support of Mike Tyson in his rape case .
Approaching the end of his tenure as president of the National Baptist Convention (as a result of term limits), Jemison selected Dr. W. Franklyn Richardson as his successor. Richardson was defeated by Dr. Henry Lyons at the 1994 convention. Unhappy with this result, Jemison concocted evidence and filed a lawsuit in an effort to overturn the election result. Eventually, the election of Dr. Lyons was upheld, and Jemison individually as well as a co-plaintiff and their counsel to pay $150,000 in punitive damages and, in a later order, required them to pay the other side's attorney fees. The court specifically found that Jemison had concocted evidence to justify the suit.