The 38-year-old journeyman, who has lost 20 of his past 22 starts, was the choice over Christian Hackenberg and Bryce Petty in what was billed as an open, three-way competition.
"He gives us the best chance to win right now," coach Todd Bowles said Monday of McCown. "He has the best grasp of the offense right now. The other two got significantly better, but he still has the best grasp of the offense right now. From his talent, he's proven it this spring and this summer."
McCown will be the Jets' fourth Week 1 starter in the past six seasons, following Mark Sanchez, Geno Smith and Ryan Fitzpatrick.
Among outsiders, McCown was cast as the early favorite, but Hackenberg received most of the work during the three-game audition. Bowles insisted he isn't disappointed with the 2016 second-round pick, who struggled in two starts.
"This has nothing to do with his development," Bowles said. "He's 22 years old. He has time to grow. He'll grow from this."
Bowles declined to name his No. 2 quarterback. He probably won't reveal that until game day Sept. 10 against the Buffalo Bills. He didn't rule out any of the quarterbacks from playing Thursday night against the Philadelphia Eagles in the preseason finale.
Hackenberg wouldn't say he was disappointed by the outcome, claiming that he benefitted from the extensive playing time.
"Coach made the decision in the best interest of the team, and we have to trust that," said Hackenberg, who saw no regular-season action as a rookie.
In the first three preseason games, Hackenberg threw two interceptions (both returned for touchdowns) and compiled only a 65.1 passer rating. In 22 possessions, he led the offense to only one touchdown. It came against the New York Giants' backups on Saturday night, when he returned to replace the injured Petty (sprained knee).
McCown sat out the last two games as Bowles employed an unconventional quarterback plan. The objective was to evaluate the two young quarterbacks, privately hoping Hackenberg would steal the job. McCown was limited to a cameo in the opener, when he led a touchdown drive on the first possession. He downplayed the lack of game action, insisting he will be ready for Week 1.
"There's a standard of play I want to achieve, and I'm looking forward to playing the best ball I've ever played," said McCown, who signed a one-year, $6 million contract in March. "That's my mindset."
Bowles suggested the decision wasn't close. Clearly, Petty outperformed Hackenberg, as he threw for three touchdowns and 250 yards against the Giants. But Petty, who appeared to be a distant third at one point in the competition, never got a chance to play with or against starters.
Petty, who was limited in Monday's practice, is expected to be available for the season opener. Petty or Hackenberg -- perhaps both -- probably will get a chance to play this season, as the Jets search for a long-term answer.
Asked if he's any closer to finding a franchise quarterback, Bowles said, "That's kind of a strange question. If you go 16-0, you've got a franchise quarterback. If you don't, I guess you don't."
Bowles: McCown gives us 'best chance'
Jets coach Todd Bowles explains that Josh McCown was chosen as the team's starting QB because he has proven himself this offseason and has the most talent at the position.