Ramos brought the curtain down on his 16-year career at the Santiago Bernabeu at the end of the 2020/2021 season.
The 35-year-old won five La Liga titles with Los Blancos, four UEFA Champions League trophies, four FIFA Club World Cups, two Copa del Reys among numerous other honours.
"I am very happy to join Paris Saint-Germain. This is a big change in my life, a new challenge and it's a day I will never forget,” Ramos told PSG’s official website.
"I am very proud to be a part of this ambitious project, to be a part of this squad with so many great players.
"Paris Saint-Germain is a club that has already proven itself at the highest level. I want to continue to grow and improve at Paris and help the team to win as many trophies as possible."
PSG chairman Nasser Al-Khelaifi added: "Today, Paris welcomes one of the greatest players of our era. We are delighted to announce that Sergio Ramos has joined us.
"Sergio is a complete footballer, one of the best defenders in the history of the game. He is a born competitor, a leader and a true professional. His vast experience and ambition is in perfect synergy with those of the club.
"I am proud to see him in a Paris Saint-Germain jersey and I know our supporters will reserve a fantastic welcome for him."
Ramos is PSG’s third summer signing after Georginio Wijnaldum and Achraf Hakimi.
