The deal is worth $65 million, with $36 million guaranteed, a source told ESPN NFL Insider Adam Schefter. Glenn stands to make $19 million in 2016 and $30 million in the first two seasons.
The Bills had assigned the franchise to Glenn, 26, on March 1. He signed the tender, worth $13.7 million, on March 4. The team had until July 15 to reach a long-term deal with Glenn under the rules of the franchise tag.
Pro Football Focus graded Glenn as the NFL's 10th-ranked offensive tackle during the 2015 season and the fifth-best in pass blocking.
A second-round pick in the 2012 draft, Glenn has started all 61 games in which he has appeared. He missed three games as a rookie because of an ankle injury.
Glenn was the Bills' recipient of the Ed Block Courage Award for the 2015 season, which is voted on by teammates. He later revealed that he underwent a procedure to remove one of his kidneys before the 2014 season.
Buffalo's starting offensive line is set to return mostly intact after the team re-signed Incognito to a three-year, $15 million deal in March.
Information from The Associated Press was used in this report.