Because of his seniority, he advanced to chairman of the Senate Finance Committee, serving for fifteen years, from 1966 to 1981, during the implementation of President Lyndon Johnson's Great Society and War on Poverty programs.

Long quietly wielded enormous power in the Senate and shaped some of the most significant tax legislation of the twentieth century.

[citation needed] As chairman of the Senate Finance Committee, Long held jurisdiction over 100 percent of all federal revenue and 40 percent of all government spending, including Social Security, Medicare, Medicaid, unemployment insurance, welfare and food assistance programs, foreign trade, and tariffs.

Because he had filled a vacancy, Long gained a few days of seniority over others in the Senate class of 1948, including Lyndon B. Johnson and Hubert Humphrey, whose terms began January 3, 1949.

Long served as President Lyndon B. Johnson's Senate floor leader, helping gain passage of the bills that enacted many of the Great Society programs, including the 1965 creation of Medicare.

"[20] Long's legislative priorities balanced a desire to help the disadvantaged, while providing tax relief for the middle class and small businesses.

[22] Long's success in maneuvering the late President John F. Kennedy's major tax reduction bill forward in early 1964 confirmed his reputation as a rising leader.

In exchange for ensuring the passage of the legislation, Long and Boggs requested that Rozelle award the next NFL expansion franchise to New Orleans.

In 1948, Clarke had tried to get the courts to forbid Long from running on both the Harry Truman and Strom Thurmond slates in Louisiana, but he failed to convince the judges.

"[29] After winning the Democratic primary, Long overwhelmed his Republican opponent, Charles Sidney Gerth (1882–1964),[30] a businessman from New Orleans.

[32] As a result of Johnson's signing of the Civil Rights Act of 1964, Long (along with more than a dozen other southern Senators, including Herman Talmadge and Richard Russell, both of Georgia) did not attend the 1964 Democratic National Convention in Atlantic City.

[33] However, Long defied conventional wisdom by delivering a television address in Louisiana in which he strongly endorsed the Johnson-Humphrey ticket, which lost the state to the Republican Barry M. Goldwater-William E. Miller electors.

He was unopposed in the general election when the presumed Republican candidate, Richard Kilbourne, the district attorney in East Feliciana Parish, withdrew from the race.

Kilbourne abandoned his campaign so that his party could concentrate on trying to elect David C. Treen to represent Louisiana's 2nd congressional district over incumbent Democrat Hale Boggs.

Louisiana Republican state chairman James H. Boyce of Baton Rouge said that the party could not find a viable candidate to challenge Long.

Mann, who now holds the Douglas Manship Chair of Journalism at LSU, later penned the 1992 book, Legacy to Power: Senator Russell B.

"[38] In 1986, Democratic U.S. Representative John Breaux of Crowley, a former legislative aide and House successor of Governor Edwards, was elected to succeed Long in the Senate.

Moore had led the balloting in the nonpartisan blanket primary but lost the general election to Breaux in a nationally Democratic year.

For a brief period following his retirement, he was a partner in the law firm of Finley, Kumble, Wagner, Underberg, Manley, Myerson & Casey, which dissolved in 1987.

He expressed his concern that moving too quickly would spark violence and divisions among the races but failing in practically improving the daily lives of African Americans.

He championed the economic interests of minorities, the poor, and the elderly by steering the landmark social welfare legislation of President Johnson's Great Society and War on Poverty.

During his 15-year tenure as Senate Finance Committee Chairman, Long exercised authority over all federal revenue collection and a vast array of entitlement spending.

His most-recognized achievements include the creation of Social Security benefits for the disabled and their dependents, Medicare and Medicaid, child support enforcement, Employee Stock Ownership Plans (ESOPS) and the Earned Income Tax Credit (EITC), the centerpiece of American poverty alleviation efforts.

Long was one of only four southern senators to vote for the Economic Opportunity Act of 1964, which included most of President Johnson's anti-poverty programs.

To break the Congressional gridlock over voting rights, he urged Presidents Kennedy and Johnson to send federal registrars throughout the South to register black voters.

[44] Long’s Senate office launched the careers of many trailblazing African Americans, including Kerry Pourciau, the first black student body president of LSU.

Martin Luther King Jr., described Long's 1965 election as the Assistant Majority Leader as a "blessing in disguise" in that he "may bring an end to the solid Southern bloc.

"[54] Following King’s assassination in 1968, Long reflected on his own father’s assassination, which he attributed to Huey Long’s repeal of the Louisiana poll tax and liberal views on race shortly before his death: "I've tried to continue some of the work he started – to help the poor people of our state and nation, both colored and whites.

He co-chaired the special Congressional Committee on Internal Revenue Taxation that determined President Nixon owed nearly half-a-million dollars in back taxes.

The funeral was held in Baton Rouge, and included eulogies delivered by his grandson, attorney Russell Long Mosely, and former colleagues Johnston and Breaux.