The Dutch midfielder left Liverpool at the end of the season as his contract expired and has opted to move to the French giants.
Wijnaldum said: "Joining Paris Saint-Germain is a new challenge for me.
"I join one of the best teams in Europe and I am determined to bring my desire and my determination to this ambitious project.
"Paris Saint-Germain has proved its status in recent years, and I am certain that together, for our supporters, we can go even further and higher."
Wijnaldum will captain the Netherlands at Euro 2020 and been tipped to link up with former national coach Ronald Koeman at Barcelona but has opted to ply his trade in Ligue 1 instead.
Wijnaldum won both the Premier League and Champions League after joining Liverpool in 2016 and Jurgen Klopp paid an emotional tribute to the player.
Klopp told the Anfield club's website: "I will miss the player he is like crazy - highest-quality ability, one of the smartest players I have ever had the privilege to coach. His contribution was off the scale, a manager's dream.
"But as a person he'll leave just as big a hole. A more giving individual you could not wish to meet. Gini is very strong and opinionated, but his motivation is only to help the team - always. His team-mates adored him and respected him in equal measure.
"His smile lit up our workplace. He was a huge part of our beating heart. Of course, he is now someone else's and on behalf of the team we wish him great success in France with PSG. It is no surprise he's joined such an amazing club. Knowing his personality, he will fall in love with the city and the team - and they with him.
"Farewell, Gini: you came, you saw, you won the lot. You're a Liverpool legend now and forever."