In 1964, Hoffa was convicted in Chattanooga, Tennessee, of attempted bribery of a grand juror, and was sentenced to eight years. This case resulted from an earlier matter, the Test Fleet case, the trial for which had been held in Nashville, Tennessee. Hoffa was implicated by one of his close associates, Edward Grady Partin, a Louisiana teamster, who went to the Federal Bureau of Investigation (FBI) with the information that led to Hoffa's conviction. Hoffa was also convicted of fraud later that same year for improper use of the Teamsters' pension fund, in a trial held in Chicago. Hoffa had illegally arranged several large pension fund loans to leading organized crime figures. He received a five-year sentence to run consecutively to his bribery sentence. Robert F. Kennedy, who had pursued Hoffa for several years, since the McClellan-led U.S. Senate Labor industry hearings of 1957, stepped down as Attorney General in 1964, after the second Hoffa conviction, to run successfully for the New York seat in the November 1964 United States Senate election.

Just before he entered prison, Hoffa appointed Frank Fitzsimmons as acting Teamsters president. Fitzsimmons was a Hoffa loyalist, fellow Detroit resident, and a longtime member (since the 1930s) of Teamsters Local 299 in Detroit, who owed his own high position in large part to Hoffa's influence. Despite this, Fitzsimmons soon distanced himself from Hoffa's influence and control after 1967, to Hoffa's displeasure. Fitzsimmons also decentralized power somewhat within the Teamsters' union administration structure. During the Hoffa era, Hoffa had kept most power in his own hands

On December 23, 1971, less than five years into his 13-year sentence, Hoffa was released from the Lewisburg, Pennsylvania prison, when President Richard Nixon commuted his sentence to time served. Hoffa had served nearly 58 months (just over one-third of his original sentence). Following his release, Hoffa was awarded a Teamsters' pension of $1.7 million, delivered in a one-time lump sum payment. This type of pension settlement had not occurred before with the Teamsters.[19]

The IBT endorsed Richard Nixon, the Republican Party's candidate, in his presidential re-election bid in 1972; in prior elections, the IBT union had supported Democratic Party nominees, but had also endorsed Nixon in 1960.[20] Suspicion was soon raised of a deal for Hoffa's release connected with the IBT's support of Nixon in 1972. It was alleged that a large sum of money, estimated to be as high as $1 million, was paid secretly to Nixon. Evidence was also alleged of a secret bribe paid in 1960.[21]

While glad to regain his freedom, Hoffa was very displeased with the condition imposed on his release by President Nixon that restricted Hoffa from participating in union activities until March 1980.[8] He accused the Nixon administration senior figures, including Attorney General John N. Mitchell and White House Special Counsel Charles Colson, of depriving him of his rights by initiating this clause; both Mitchell and Colson denied this. It was likely imposed upon Hoffa as the result of requests from senior Teamsters' leadership, although IBT President Frank Fitzsimmonsalso denied this.[22]

Hoffa sued to invalidate the non-participation restriction, in order to reassert his power over the Teamsters, and John Dean, former White House counsel to President Nixon, was among those called upon for depositions in 1974 court proceedings.[23] Dean, who had become famous as a government witness in prosecutions arising from the Watergate scandal by mid-1973, had drafted the non-participation clause in 1971 at Nixon's request. Hoffa ultimately lost his court battle, since the court ruled that Nixon had acted within his powers by imposing the restriction, as it was based on Hoffa's misconduct while serving as a Teamsters' official.

Hoffa faced immense resistance to his re-establishment of power, from many quarters, and had lost much of his earlier support, even in the Detroit area. As a result, he intended to begin his comeback at the local level, with Local 299 in Detroit, where he retained some influence.[19]

In 1975, Hoffa was working on an autobiography titled Hoffa: The Real Story, which was published a few months after his disappearance. He had earlier published a 1970 book titled The Trials of Jimmy Hoffa.

Hoffa disappeared at, or sometime after, 2:45 pm on July 30, 1975, from the parking lot of the Machus Red Fox Restaurant in Bloomfield Township, an affluent suburb of Detroit. According to what he had told others, he believed he was to meet there with two Mafia leaders: Anthony Giacalone and Anthony Provenzano.[24] Provenzano was also a union leader with the Teamsters in New Jersey, and had earlier been quite close to Hoffa. Provenzano was a national vice-president with IBT from 1961, Hoffa's second term as Teamsters' president.[18]

When Hoffa did not return home that evening, his wife reported him missing. Police found Hoffa's car at the restaurant, but there was no sign of Hoffa himself or any indication of what happened to him. Extensive investigations into the disappearance began immediately, and continued over the next several years by several law enforcement groups, including the FBI. The investigations did not conclusively determine Hoffa's fate. For their part, Giacalone and Provenzano were found not to have been near the restaurant that afternoon, and each denied they had scheduled a meeting with Hoffa.[25]

Hoffa was declared legally dead in 1982, on the seventh anniversary of his disappearance, when he would have been aged 69.[2][18] His disappearance gave rise to many rumors and theories.

James Riddle "Jimmy" Hoffa