Collins reportedly informed his players in a clubhouse meeting prior to the game against the Philadelphia Phillies that it would be his last as manager.
When Collins was waiting to walk out the lineup card to the umpires, a majority of the players stopped to shake hands or bump fists with him. As he returned to the dugout, the players lined up and applauded him.
The 68-year-old Collins has been the subject of speculation over whether or not he would be back. He guided the team to the 2015 World Series -- losing to the Kansas City Royals -- but the Mets missed the postseason last season and were a disappointing 70-91 entering Sunday's game.
Collins, who was the oldest manager in the majors, is expected to remain with the team in a front office role.
Before the contest, Collins didn't let on that he was about to resign.
"It's baseball," Collins said. "I've spent my whole life in it. There's good days, bad days, good years and bad years. You have to be able to deal with them all. You can't just ride the wave all the time. You have to move on."
Collins had a 551-582 record in seven seasons with the Mets entering Sunday's game. Overall, he was 995-1,016 in 13 seasons, including stints with the Houston Astros (1994-96) and the then-Anaheim Angels (1997-99).