On March 4, 2008, Favre formally announced his retirement. Although Favre stated that he had been willing to play another year, he felt that another season would only be successful if he led his team to another Super Bowl victory. He added the chances for a Super Bowl win were small, and that he was not up for the challenge. At his press conference, Favre openly wept about leaving the NFL. He stated that his decision, regardless of what was being said in the media, had nothing to do with what the Packers did or didn't do. Seeming to contradict statements made by his agent, Bus Cook, Favre said that his decision to retire was based on the fact that he did not want to play anymore. He said during the conference, "I know I can play, but I don't think I want to. And that's really what it comes down to."
On July 2, 2008, it was reported that Favre was in contact with the Packers about a possible return to the team. On July 11, 2008, Favre sent a letter to the Packers asking for his unconditional release to allow him to play for another NFL team. Packers general manager Ted Thompson announced he would not grant Favre an unconditional release and reaffirmed the organization's commitment to Aaron Rodgers as its new quarterback. Complicating matters was Favre's unique contract giving him the leverage to void any potential trade by not reporting to the camp of the team he might be traded to if the Packers elect to go that route.
In the second part of the interview, which aired on July 15, Favre expressed his frustration with Packer management, spoke of his sympathy for successor Aaron Rodgers's predicament, and affirmed he is 100 percent committed to playing football in 2008.
FOXSports.com's Jay Glazer reported on July 16, 2008, that the Packers filed tampering charges against the Minnesota Vikings with the league office, alleging improper communication between Vikings offensive coordinator Darrell Bevell and Favre, although one source suggested that Favre may have been in contact with Vikings head coach Brad Childress. After an investigation, NFL Commissioner Roger Goodell ruled there had been no violation of tampering rules.
Favre formally filed for reinstatement with the NFL on July 29, 2008, and his petition was granted by Commissioner Goodell, effective August 4, 2008. Favre then flew to Green Bay to report to Packers training camp. After a lengthy meeting with head coach Mike McCarthy and general manager Ted Thompson, however, both sides agreed it was time for Favre and the organization to part ways. McCarthy sensed Favre was not in "the right mind-set" to resume playing for the Packers, while Favre felt that his relationship with Packer management had deteriorated to the point that a return to the team would be untenable.
The Packers had announced plans to retire Favre's #4 jersey in the 2008 season opener. Those plans were dropped when he announced plans to return to the NFL. In March 2009, the Packers indicated that the team still intends to retire Favre's number, but due to the circumstances surrounding his departure from the team, no timeline had been set.
After negotiations with both the Tampa Bay Buccaneers and New York Jets, the Packers traded Favre to the Jets on August 7, 2008, in exchange for a conditional fourth-round pick in the 2009 NFL Draft with performance escalation.
In his Jets debut, Favre passed for 194 yards and two touchdowns in a 20–14 victory over the Miami Dolphins. In Week 4, he threw six touchdowns against the Arizona Cardinals, a personal best and one shy of the NFL record. This performance led to him being selected as the FedEx Air Player of the Week. By Week 12, the Jets had compiled an 8–3 record, including a 34–13 win over the previously undefeated Tennessee Titans. However, the Jets lost four of the last five games of the season, including the final game against the Miami Dolphins, who had acquired quarterback Chad Pennington after he was released from the Jets to make room for Favre. In those five games, Favre threw eight interceptions and only two touchdown passes, bringing his season total to 22 of each. Favre had complained of shoulder pain and had an MRI performed on December 29, 2008, which revealed a torn biceps tendon in his right shoulder. After the 2008 season had ended, in mid January 2009, Favre told Jets General Manager Mike Tannenbaum, "it may be time to look in a different direction" regarding the quarterback position. On February 11, 2009, Favre informed the Jets that he was retiring after 18 seasons. He remained part of the Jets organization until April 28, 2009, when the Jets released Favre from his contract, thus allowing him to sign anywhere he wanted. By May 2009, he was officially cut from the Jets Reserve/Retired list. In September 2009, Favre again made Jets news, as the NFL learned that the Jets were aware that Favre injured his arm in the 11th game of the 2008 season, and fined the Jets $125,000 for not reporting the injury in any of the Jets' five final games.