Beckham joined the French club after rejecting other offers. No details were given on how much the 37-year-old star will be paid or which charity will get the money.
"It's something we (decided) together; it's one of the things we talked about from the start. But this all happened so quick," Beckham said. "I thought what a great idea it would be, that the salary would go to a children's charity in Paris."
Beckham's glamorous career has seen him win titles with Manchester United, Real Madrid and the Los Angeles Galaxy.
"Every club I have played for throughout the world, I have been successful with. I have been successful with Manchester United, and I have always said that I would never want to play for another English club," Beckham said. "It's the team that I support, that I always dreamt of playing for."
Beckham recently finished a six-year stint in the United States with the Galaxy in Major League Soccer. Whether he can still be a force in European soccer is uncertain.
"I am very lucky. I am 37 years old and I got offered a lot of offers, more offers now than I have probably had in my career, at my age," Beckham said. "I am very honored about that. I chose Paris because I can see what the club are trying to do, the players the club are trying to bring in. It's an exciting city, always has been, always will be."
The immaculately dressed Beckham was a model of elegance and calm as camera crews and photographers jostled for position amid the frenzy. He joked that he feels much younger than his age.
"To be the elder statesman, I'm very proud of that," he said. "No matter what my age is, I still feel 21 years old -- most days."
Although Beckham's deal runs out in June, he intends to keep playing, although whether that will be with PSG remains to be decided. He is, however, eager to have a long-term role at the club.
"We slightly brushed over it, a long-term partnership is what we have looked for," he said. "Short term is playing, but long term is something we are very proud to be part of this organization that will grow and become one of the biggest in Europe."
Beckham was close to joining PSG last year, discussing a potential move with a club desperately chasing a big name to match its sudden allure and seemingly endless funds from its Qatari backers.
But the move fell through and PSG moved on to other targets, landing striker Zlatan Ibrahimovic and AC Milan teammate Thiago Silva as well as Napoli winger Ezequiel Lavezzi and Brazilian prodigy Lucas.
"I felt last year that I still had something to achieve in Los Angeles. I won the championship in the last year of my contract," said Beckham, adding that the time was not right. "So we parked it and decided that right now is the right time because I was at the end of my contract last year. I accepted one more year in Los Angeles, I won another championship, another trophy in Los Angeles and I believe it was the right time to leave."
He said that about 1 a.m. Thursday the move was finally done. And shortly before noon, he made the short flight to Paris.
"Right now, I have a few things to sort out with my children and the schooling and a few other things," he said. "I have been training at Arsenal. My fitness won't take long to get up to speed. I definitely won't be fit for next Friday. A few weeks and I'll be up to speed."
While he was on the flight, Beckham agreed on a novel way of putting his big salary to good use.
"We decided on something that is quite unique -- I won't receive any salary. We have decided that my salary will go towards a local children's charity in Paris. And that's one of things we are very excited and proud to be able to do," he said. "It's something I'm not sure has been done before, and it's something I'm very passionate about, children and the charity side of things, and so are the club. We came together and it's something special."
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