The 37-year-old midfielder was available on a free transfer following the expiration of his contract with LA Galaxy in December and signed a deal with the Ligue 1 leaders after undergoing a medical in Paris on Thursday afternoon.
Beckham, who had been training with Arsenal recently to maintain his fitness, attracted offers from across the globe but was unveiled as the latest superstar to join PSG in a press conference attended by sporting director Leonardo and president Nasser al-Khelaifi at Parc des Princes.
"We've been talking about it [the deal] for quite a while," Beckham said. "I'm delighted it's happened.
"I'm lucky - I got more offers at 37 than I'd had in my career. I chose Paris because I can see what the club are trying to do. It's an exciting city, but now there is a club that is going to have a lot of success in the next 10, 15, 20 years.
"I'm very honoured that I'm part of this - honoured to be part of the future of PSG."
Beckham also announced that his entire salary for his five-month stay in the French capital will be going to a children's charity.
"One of the reasons I wanted to come to Paris was we decided on something quite unique," he said. "I won't receive a salary.
"I'm very passionate about children and charity and so are the club. I don't think something like this has been done before."
The fact PSG face Valencia in the last 16 of the Champions League and currently sit top of the Ligue 1 table on goal difference made a move to France an attractive sporting proposition and Beckham will also link up again with coach Carlo Ancelotti and Leonardo having worked with both men during loan spells with Milan in 2009 and 2010.
PSG have financial clout too - they are Qatari-owned and have been the highest-spending club in Europe in the past year, convincing Beckham to turn down 12 formal offers from around the globe including South America, North America, South Africa, Russia, China and the Middle East as well as Europe.
Beckham also said he rejected a possible return to the Premier League due to his history with Manchester United.
"I had offers from Premiership teams," he said. "I've always said that I would never want to play for another English club because I have a lot of history with Manchester United."
PSG president Al-Khelaifi said: "David refused a lot of clubs from around the world, so we're very happy to have him.
"We have a big project and are trying to reach our dream - to become one of the biggest clubs in Europe."
Beckham, who won 115 caps for England, had been available as a free agent after leaving Galaxy December. He won two MLS Cup finals in five-and-a-half years with the American club.
Eurosport's French editor Cedric Rouquette said of the deal: "It is probably for marketing issues. PSG is looking for the biggest impact possible on Earth to let everybody know that a huge team is coming.
"Beckham will be a 'noise amplifier', probably the best possible to touch a massive audience around the world, on each continent.
"The position where Beckham is able to play is probably the one where PSG have the least needs. On the right side of the midfield, they have Lucas Moura, Lavezzi and Menez. For central midfield, there is Verratti, Thiago Motta, Matuidi, Chantôme.
"Old players usually have difficulty making an impact in Ligue 1 and PSG are fighting for the title so Carlo won't have that many opportunities to let him play just to make appearances.
"But if there are any, then his wonderful right foot could be useful. No one except Zlatan in the PSG can offer anything like that precision of passing."
A move to Paris is just the latest twist in a prestigious career that started when he emerged from the Manchester United academy and won six Premier League titles, two FA Cups and the Champions League in 1999.
He later joined Real Madrid, winning La Liga in 2007, before announcing a shock move to Galaxy in 2007.