Rivers told the San Diego Union-Tribune about his decision to retire late Tuesday night.
"It's just time," Rivers said. "It's just right."
The 39-year-old quarterback completed 68% of his throws for 4,169 yards, 24 touchdowns and 11 interceptions in 16 starts this season. He led the Colts to an 11-5 record before they lost to the Buffalo Bills in the first round of the playoffs.
Rivers spent the first 16 years of his career with the Los Angeles Chargers. He signed a one-year, $25 million contract last off-season with the Colts.
Rivers ranks No. 5 all-time in passing yards and touchdown passes. The eight-time Pro Bowl selection also is the Chargers' franchise leader in passing yards and touchdown passes.
He started 240 consecutive games to end his career, the second-longest streak for a quarterback in NFL history. Hall of Famer Brett Favre started 297 consecutive games.
Rivers will take over as the head football coach at St. Michael Catholic High School in Fairhope, Ala., after his retirement becomes official. He announced last May that he would assume that role after his NFL career.
"I can sit here and say, 'I can still throw it. I love to play,' " Rivers said. "But that's always going to be there. I'm excited to go coach high school football."
Rivers -- the 2013 Comeback Player of the Year -- ends his career with a 134-106 record as a starter. He went 5-7 in the playoffs and never appeared in a Super Bowl. He led the NFL with 34 touchdown passes in 2008 and led the league in interceptions in 2014 and 2016.