Clarke had tried 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, and Long's votes on each slate were counted. According to William J. "Bill" Dodd, who was running for lieutenant governor at the time, Judge Leander Perez of Plaquemines Parish, a segregationist and conservative member of the Democratic State Central Committee, wanted the panel to tap Clarke as the official "Louisiana Democratic" senatorial nominee. Had Perez pursued that strategy, Clarke may have won the seat on combined Thurmond-Dewey coattails. Dodd claimed that Governor Earl Long reconciled with Perez on other matters of importance to Perez to make sure that Russell Long got the "Louisiana Democratic" position on the ballot.
Because the 1948 election was for a two-year unexpired term, Long had to run again in 1950 for his first full six-year term. That year, he had no trouble defeating a minor Republican opponent, Charles S. Gerth, a businessman from New Orleans. Long polled 220,907 (87.7 percent) to Gerth's 30,931 (12.3 percent).
Long's contributions to the United States' tax laws include the Earned Income Tax Credit, a program aimed at reducing the tax burden on poor working families, and Employee Stock Ownership Programs (ESOPs), employee benefit plans designed to allow employees to invest in the stock of their employers. In the year 2006, the Earned Income Tax Credit lifted more than four million people above the poverty line and was called “the nation’s most effective antipoverty program for working families.” Long also initiated the provision that allows a taxpayer to allocate $1 of taxes for a presidential campaign-financing fund (the "dollar checkoff").
After his election in 1948, Long never again faced a close contest for reelection. In 1962, he defeated attorney Philemon A. "Phil" St. Amant in the Democratic primary, 407,162 votes (80.2 percent) to 100,843 votes (19.8 percent). He then defeated Republican challenger Taylor W. O'Hearn, a Shreveport attorney and accountant, with 318,838 votes (75.6 percent) to 103,066 (24.4 percent). Both St. Amant and O'Hearn challenged Long from the right.
In 1964, 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. The action had no impact on Long's future, however, as Republicans declined to challenge his reelection in 1968, 1974, and 1980.
Democratic senators named him the party whip in 1965. He lost his leadership position in 1969 to Edward M. Kennedy of Massachusetts. He had especially good relations with both of his senatorial colleagues from Louisiana, first Allen J. Ellender and, then, J. Bennett Johnston, Jr., who like Long was born in Shreveport.
In 1974, Long defeated state Insurance Commissioner Sherman A. Bernard of Westwego in Jefferson Parish, 520,606 (74.7 percent) to 131,540 (18.9 percent), in the Democratic primary. (Another 44,341 (6.4 percent) went to a third candidate, Annie Smart.) State Republican Chairman James H. Boyce of Baton Rouge told the Congressional Quarterly Weekly Report that Louisiana Republicans were "so badly outnumbered that we can't find enough candidates to run in local elections". Boyce noted that the party could not find a suitable candidate to challenge Long.
In 1980, Long defeated State Representative Louis Woody Jenkins of Baton Rouge, 484,770 (57.6 percent) to 325,922 (38.8 percent). Jenkins was a Democrat in the jungle primary that year, but he later became a Republican and ran once more for the Senate in 1996, only to lose by some 4,000 votes. In the 1980 campaign, Long's friend and colleague, Robert J. "Bob" Dole, the Kansas Republican who had been his party's vice presidential nominee in 1976 and who would be the presidential nominee in 1996, cut a television commercial for Long in the race against Jenkins, who had also lost a challenge to Johnston in 1978. Dole and Long were both running for reelection that year. The 1980 jungle primary was the last time Long's name was on a ballot.
In 1986, Democratic Congressman John Breaux of Crowley was elected to succeed Long in the Senate. Breaux defeated the Republican Congressman W. Henson Moore, III, of Baton Rouge, who had served in the House since 1975, in the general election after having trailed Moore in the primary election. Breaux served three terms in the Senate; when he left the body he was as popular as Long had been. Breaux, unlike Long, however, did not secure the election of his chosen successor. The seat went Republican in 2004, with the victory of Congressman David Vitter of the New Orleans suburbs.
After he considered and rejected a run for governor of Louisiana, Long retired from the Senate in 1987. Summing up his career in the Senate, Ronald Reagan called him a "legend" and "one of the most skillful legislators, compromisers and legislative strategists in history." The Wall Street Journal once called Long "the fourth branch of government." He remained in Washington, D.C., as a highly sought-after lobbyist after his retirement. For a brief period of time following his retirement, he was a partner in the law firm of Finley, Kumble, Wagner, Underberg, Manley, Myerson & Casey, which dissolved in 1987. He later founded the Long Law Firm, where he remained a partner until his death. Long also served on the Board of Directors of The New York Stock Exchange, Lowe's Companies, Inc. and Metropolitan Life Insurance Company.