"Philip is one of the most decorated quarterbacks in the NFL and we are fortunate to add an experienced player of his caliber to our organization," Colts general manager Chris Ballard said in a statement. "His familiarity with our coaching staff and offensive system in addition to his experience were attractive qualities during our evaluation process. Philip is a fierce competitor and his veteran leadership will be crucial in the continued development of our young roster."
Indianapolis did not release the terms of Rivers's contract, but ESPN's Adam Schefter previously reported the veteran QB agreed to a one-year deal with the team worth $25 million.
Rivers, 38, played the first 16 years of his career with the Chargers, but the team publicly announced in mid February that both parties were moving on from each other.
"As we talked through various scenarios, it became apparent that it would be best for Philip and the Chargers to turn the page on what has truly been a remarkable run," GM Tom Telesco said.
In the team's statement, Rivers said he was appreciative of his time with the club.
"I never took for granted the opportunity to lead this team out on to the field for 235 games," he said. "We had a lot of great moments, beginning in San Diego and then finishing in L.A. I wish my teammates and coaches nothing but the best moving forward."
The eight-time Pro Bowler has thrown for nearly 60,000 career yards and is three passing touchdowns shy of 400. He has played in only 11 career postseason games, however, winning five of them.
Last season, Rivers started all 16 games for the fourteenth consecutive year. He tossed just 23 touchdowns, his fewest since 2007, and threw 20 interceptions, tied for the second-most he had thrown in a single season.
The Colts finished 7–9 last season led by quarterback Jacoby Brissett, who became the starter after Andrew Luck suddenly retired late in the preseason.