Still, as Glennon enters his first season with the Cardinals and fifth overall in the NFL, he understands that there are no givens at the most demanding position in the game.
"Everyone wants to be out there playing, but at quarterback it's a unique situation because only one guy can play," Glennon recently told the team's official website. "That dates back to my time in college when I was behind Russell Wilson [at North Carolina State] for three years. You feel like you're a pretty good player yourself, but there's only room for one guy. You just have to keep everything in perspective and realize I'm still living the dream."
Glennon's dream appeared to come true when he signed a three-year, $45 million contract -- $18 million guaranteed -- with the Chicago Bears in March 2017 after spending his first three seasons in Tampa Bay.
A third-round pick of the Buccaneers in 2013, Glennon lasted only four games as the starter with the Bears before he lost the job to rookie Mitch Trubisky, the No. 2 overall selection in the 2017 NFL Draft.
Chicago released Glennon after the season and he signed a two-year contract with the Cardinals, who also signed oft-injured Sam Bradford to a one-year deal.
The quarterback derby became more crowded when Arizona traded up five spots to draft UCLA quarterback Josh Rosen with the 10th overall selection in the 2018 NFL Draft.
Bradford is expected to open the season as the starter, leaving Glennon to jockey with Rosen for the backup job.
"I've been in that backup role more than the starter, so I'm comfortable with it," said Glennon. "I understand my role, and what my job is to help this team. That's to both compete and help these two guys out."
Last season, Glennon completed 93 of 140 passes (66.4 percent) for 833 yards, four touchdowns and five interceptions with three lost fumbles. He has made 22 career starts -- 13 of those coming in his rookie season -- so he is prepared for anything.
"That's what I feel like I've done over the past few years, always prepare and be ready for that opportunity," Glennon said. "When I was the backup in Tampa, it never really came. You just never know. I know Arizona has had that come up a lot recently. You have to go in with the mindset of, 'I have to be ready to go.'"