Waller attempted to reform the position and provoked the ire of local law enforcement for aggressively prosecuting several cases.

In 1964, he twice prosecuted Byron De La Beckwith for the murder of civil rights activist Medgar Evers, with both trials resulting in deadlocked juries.

[7] One of his sons, Bill Waller Jr., later served as Chief Justice of the Supreme Court of Mississippi and made an unsuccessful bid for gubernatorial office in 2019.

[11] As the district attorney, Waller prosecuted Byron De La Beckwith in the murder of civil rights advocate Medgar Evers in two trials in 1964, both of which resulted in mistrials due to deadlocked juries.

[12] Waller did not approve of Evers' activism and did not view the trials as a means to denounce Jim Crow racial segregation, but saw it as an opportunity to demonstrate that laws would be upheld in the state.

[14] Fears among white Mississippians that Waller was a "liberal" for trying De Le Beckwith led his firm to lose clients.

[15] Numerous observers speculated that the trials would damage his political prospects, with The New York Times writing in February 1964 that "He may have put his career on the block by his tireless prosecution of the case".

[16] Despite this, he won some national acclaim for convincing several white jurors to vote for conviction and ingratiated himself to Mississippi's black population.

[20] Waller attempted to straddle both sides of the issue, becoming the first Mississippian gubernatorial candidate to ever publicly condemn the Ku Klux Klan while also criticizing civil rights activists and praising the work of Citizens' Councils.

[18][22] In 1971, Waller mounted another campaign for gubernatorial office, facing Lieutenant Governor Charles L. Sullivan, Jimmy Swan, and four others in the Democratic primary.

[23] While Swan resorted to racist appeals and declared his opposition to integration,[24] Waller and Sullivan focused on other matters, though they both affirmed their support for "law and order" and segregation academies, and opposed desegregation busing.

[28] He hired Deloss Walker of Memphis, Tennessee, as a campaign consultant, beginning a trend of gubernatorial candidates using out-of-state advertising agencies which lasted into the 1980s.

[18] In the general election Waller faced two independents, civil rights activist Charles Evers (the brother of Medgar) and segregationist judge Tom P.

[31] Evers was the other major candidate and, despite the fears of public observers, the campaign was largely devoid of racism and both him and Waller avoided negative tactics.

[35] Waller appointed several blacks to positions in state government and his staff,[36] the first time this had been done since the Reconstruction era,[37] but most had no history of political activity.

Waller had served as legal counsel for the convicted murderer prior to his election, and his action drew scrutiny from blacks.

[43][44] The following week, he declared that Medgar Evers Day would be celebrated on the tenth anniversary of the civil rights leader's death,[44] but then did not attended the formal ceremony marking the date.

Waller rarely informed Winter when he was leaving the state, meaning the latter often discovered that he was to be acting governor from newspaper stories.

[46] Waller disregard Junkin's advice to leave most matters of public importance to the legislature, and came into frequent conflict with the body, vetoing 32 bills during his tenure.

[32] Waller endorsed the funding of a $600 million highway program, but the proposal had been devised during his predecessor's tenure[32] and declining government revenues led it to be later suspended.

[61] As part of this, Waller signed a law which permitted the Loyalist faction to choose between electing delegates in presidential primaries or nominating them at district conventions.

[64] On March 10, 1978, he hosted a press conference in which he criticized Eastland for sharing his intent to seek reelection to the U.S. Senate, saying "I happen to believe a young man with some stamina and vigor is needed.

[66] Waller sought the Democratic nomination for governor again in 1987,[67] running on a platform of increased highway construction, program budgeting for state agencies, and the revival of referendums.

[49] Historian David Sansing opined that "Waller was elected at a crucial time in the state's history and his constructive leadership helped chart a new direction for Mississippi.

"[4] Minor wrote that "the greatest value of the Waller years" was in his creation of "harmony between blacks and whites in Mississippi's highly complex society".

[49] Journalist Adam Nossiter reflected, "Waller was not too keen on the integrationist goals of the civil rights movement, but Jim Crow disturbed his ideals of justice and fair play.