"I'm going into my 17th season of professional football, and for the first time I feel like I'm going to be the guy and have an opportunity to take a team as far as we can go," said Flutie, who's joining his fourth NFL team in a career that also included eight seasons in the CFL.
He replaces Ryan Leaf, who was released and claimed off waivers by Tampa Bay.
Although neither side would discuss contract details, Flutie's signing bonus is believed to be about $3 million.
Flutie is reunited with general manager John Butler, who as GM of the Buffalo Bills brought the 5-foot-10 quarterback back into the NFL in 1998, signing him as a free agent from the CFL.
Butler was hired as Chargers GM on Jan. 5 and has quickly started to reshape a team that was an NFL-worst 1-15 in 2000. His biggest coup was signing unrestricted free agent defensive end Marcellus Wiley from the Bills to a $40 million, six-year contract, the biggest in team history.
Flutie becomes the starter for a team that is expected to take Michael Vick with the top pick in April's draft.
"Doug's main deal will be to play quarterback for this team and win," coach Mike Riley said.
Flutie was 21-9 in three seasons with the Bills but didn't survive Buffalo's long-running QB controversy. He was released last week after the Bills decided to go with Rob Johnson.
"I was frustrated for a few hours but then I realized that it just opened a bunch of other doors for me," Flutie said.
"It may be the best thing that ever happened to me, to move on. Hopefully it will be the best thing for both Rob and I. Rob has his team and now I have mine, and maybe we'll meet way down the road."
They'll certainly meet in the fall, because the Chargers are scheduled to play host to the Bills. The exact date will be set in the spring.
Leaf was 4-14 as a starter in his turbulent three years with San Diego. He threw 33 interceptions and lost nine fumbles while throwing just 13 touchdown passes.
On the same day they released Leaf, the Chargers signed Dave Dickenson from Calgary of the CFL, one of Flutie's old teams.
The Chargers hope Flutie can add some stability to a position that's been a disaster the last 3 1/2 seasons. Sinc Stan Humphries suffered what turned out to be a career-ending concussion in the ninth game of 1997, six Chargers QBs have combined to throw 99 interceptions and just 47 touchdowns.
Even before signing Flutie, Butler had spent $71.6 million on defensive free agents Wiley and cornerbacks Ryan McNeil and Alex Molden.
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