McCown, who turns 40 on July 4, played for the New York Jets the last two seasons before deciding to retire.
"I guess it just goes to show that you don't always get to choose your own path," McCown wrote. "But looking back, I'm proud of how my career has gone. I don't shy away from the journeyman label. I embrace it, full force. Because it's been one heck of a journey."
After stepping away from the league, it was announced that McCown is joining ESPN as an NFL analyst. He will make his debut Wednesday on NFL Live.
"I am excited to make the transition into broadcasting with ESPN which will allow me to still be involved with the game I love," McCown said in a statement. "I look forward to bringing ESPN viewers the unique insights that I have gained throughout my career."
McCown played for eight different teams over 17 years, starting with the Arizona Cardinals in 2002. He spent four seasons with the Cardinals, then played for the Detroit Lions, Oakland Raiders and Carolina Panthers. He also joined the Miami Dolphins and San Francisco 49ers, but never played in regular-season games for them.
McCown spent one season out of the league before signing with the Chicago Bears in 2011. He posted a career-best 109.0 passer rating with the Bears in 2013, throwing 13 touchdowns and only one interception in eight games (five starts).
The journeyman signal-caller bounced around to the Tampa Bay Buccaneers (2014) and Cleveland Browns (2015-16) before spending two seasons with the Jets. He started 13 games in 2017 and had a career-high 18 passing touchdowns, but was benched for first-round pick Sam Darnold in 2018.
"No matter what team I was on, I tried to serve it to the best of my ability, and I tried to influence my team in a positive manner," McCown wrote. "I hope I did that. And I made sure that when my number was called, I was prepared, and I gave it everything I had, every time."
McCown had 17,707 passing yards, 98 touchdowns, 82 interceptions and a 79.7 passer rating in his NFL career.