He revealed his decision via social media:
Long spent two seasons with the Eagles after a one-year run with the New England Patriots.
During his first season in Philadelphia, Long registered 28.0 tackles and 5.0 sacks en route to helping the Eagles beat the Patriots in Super Bowl LII.
Long then recorded 23.0 tackles and 6.5 sacks in 2018 and helped Philly return to the playoffs.
Following an eight-year stint with the St. Louis Rams (who selected him No. 2 overall in the 2008 NFL draft), the veteran defensive end signed a one-year deal with the Pats prior to the 2016 season.
Although he only started seven games, Long enjoyed a productive campaign with 35.0 tackles, 4.0 sacks, one forced fumble and one fumble recovery.
Long also appeared in the first three playoff games of his career, making a sizable impact in New England's Super Bowl LI victory over the Atlanta Falcons.
Long's decision to sign with Philadelphia was detrimental to New England's pass rush, but it represented an upgrade for the Eagles, who already had some solid sack artists in Brandon Graham, Fletcher Cox and Derek Barnett.
Despite doing very little winning with the Rams, Long transitioned seamlessly to New England, and he continued his winning ways with the Eagles by helping them reach the playoffs for the first time since 2013.
Long's best run of success from a statistical perspective came from 2010 through 2013 in St. Louis when he recorded 8.5 or more sacks in each of those four seasons. He will depart the NFL with 70.0 career sacks to his credit.
His retirement leaves a hole in Philadelphia's front seven, but the Eagles have some talented, up-and-coming players on defense who should help fill the void.