He and Eastland supported the Dixiecrat ticket in 1948 headed by Strom Thurmond,[1] and signed the Southern Manifesto, which called for massive resistance to the Supreme Court ruling in Brown v. Board of Education.

[4] In 1928, Stennis obtained a law degree from the University of Virginia at Charlottesville, where he was a member of Phi Beta Kappa, and Alpha Chi Rho fraternity.

[9] Upon the death of Senator Theodore Bilbo in 1947, Stennis won the special election to fill the vacancy, winning the seat from a field of five candidates (including two sitting Congressmen, John E. Rankin and William M. Colmer).

[10] The declaration of support for civil rights at the Democratic National Convention had resulted in Southern members dissatisfied with the move and seeking to espouse their own ideology in the form of a rebellion, Stennis and Eastland being the only sitting senators to openly back the movement.

[23] In early 1962, as the Justice Department retaliated against a Mississippi official charged with refusing to register black voters, Stennis led Southern senators in opposition to the Kennedy administration's literacy test bill during a debate on the measure.

[28] In August 1967, Stennis advocated for an expansion of bombing North Vietnam to hasten what he believed would be the war's conclusion, adding that either restrictions or a pause could be a mistake.

[30] In December, Stennis supported the creation of a special commission by President Richard Nixon with the intent of investigating alleged Vietnamese civilian slayings at the hands of American soldiers.

[31] In July 1968, Stennis served as floor manager of a bill intended to ease congestion that had throttled American airports in recent days by providing increased equipment and personnel, publicly saying the legislation had been put off for too long.

[34] On February 12, White House Press Secretary Ronald L. Ziegler said President Nixon was in favor of the North and the South being treated equally on the issue of segregation, refusing to interpret his remarks as an endorsement of the Stennis desegregation amendment.

Stennis said the question "must and should be decided as promptly as possible because a political decision is being made to continue the integration efforts in the South but leave the other areas of the country virtually untouched.

[39] In February 1970, Stennis was named as one of the members of Congress to sit on a subcommittee created to study whether the United States needed another nuclear‐powered aircraft carrier priced at $640 million.

[42] In July 1972, Stennis said it was essential that Congress appropriate $20.5 million for the funding of military supplies and research to meet the basic requirements for the national defense program.

[46] On February 9, Stennis met privately with Charles Radford, a member of the United States Navy who admitted removing documents from the files of Henry Kissinger in addition to delivering them to the Pentagon.

[52] Later that month, Wisconsin Senator William Proxmire requested Stennis delay action on the nomination of Albert Hall as Assistant Secretary of the Air Force.

[61] In July, President Carter sent Stennis a letter stating his decision on deployment would come after he received reports on the neutron bomb from the Pentagon and the Arms Control and Disarmament Agency.

[62] After the November death of Arkansas Senator John L. McClellan, Stennis was seen as a potential chairman of the Defense Appropriations Subcommittee in the event Warren Magnuson did not attempt to take the position himself.

[67] In April 1970, in response to the Nixon administration's choice to back efforts by the South Vietnamese in Cambodia,[68] senators made moves toward ending funding for American military aid there.

Stennis and Michigan Senator Robert P. Griffin described the operation as one limited in scale and with the purpose of destroying sanctuaries of the North Vietnamese and Vietcong in Cambodia on the South Vietnam border.

"[71] In September, the Senate voted on the McGovern–Hatfield Amendment, a proposal that would have required the end of military operations in Vietnam by December 31, 1970, and a complete withdrawal of American forces halfway through the next year.

Stennis argued the amendment was constitutional and that Congress had "the sole power to appropriate money" but opposed it on the grounds that it would harm the American negotiating position.

Stennis said the legislation would have caused the creation of two classes of soldiers where one group could fight and the other could not while arguing that any army unit "would be rendered inoperative if each man's record had to be reviewed by the commanders before they acted in an emergency".

[79] In April 1973, Stennis, in a statement drafted at Walter Reed Army Hospital while he was still recovering from gunshot injuries, called for legislation that would prevent the President from restoring American troops in Vietnam without congressional backing.

[80] The Senate, in a vote of 71 to 18, approved a similar measure in July, barring the president from being able to commit American armed forces to future foreign hostilities without the consent of Congress.

Stennis sent a letter to Edmund Muskie advising that cluttering the "war powers bill with other matters" would give the measure the possibility of overriding a veto.

[81] In May 1974, Stennis announced the Senate Armed Services Committee had approved $21.8 billion in weapons production and research for the upcoming fiscal year, a 5.6 percent decrease in the funding requested by the Nixon administration.

[82] In May 1970, Stennis argued against an amendment by Frank Church and John Sherman Cooper that if enacted would prohibit funds for retaining American troops in Cambodia, telling Senate Foreign Relations Committee Chairman J. William Fulbright he did not understand how a president could select a date without assurance there would be no reversals in battle.

Stennis called the choice to declare war "too big a decision for one mind to make and too awesome a responsibility for one man to bear" and that he was aiming for Congress to give consideration to the idea posed in his measure for roughly a year before drafting any legislation.

With multiple amendments still needing to be voted on by the chamber, Senate Majority Leader Mike Mansfield afterward announced that Stennis, Hugh Scott, and himself would present a petition to end a debate.

Earlier, as a prosecutor, he sought the conviction and execution of three black sharecroppers whose murder confessions had been extracted by torture, including flogging, hanging, and strangulation.

(It has since been surpassed by Robert Byrd, Strom Thurmond, Ted Kennedy, Daniel Inouye, Patrick Leahy, Orrin Hatch, and Chuck Grassley, leaving Stennis ninth).