PSG confirmed the signing of mercurial forward Messi on a two-year deal on Tuesday, with the option of a further year.
The six-time Ballon d'Or winner left Barcelona as the LaLiga giants were unable to afford to keep the 34-year-old.
Messi scored 672 times in 778 appearances for the Blaugrana, winning the Champions League four times and claiming 10 LaLiga titles.
PSG president Al-Khelaifi believes he will add many more honours at PSG, declaring the signing of Messi to be "just the start".
"I am very happy and proud to present Lionel Messi as PSG player. It is an historic day for the club and football world and is a fantastic moment for us," Al-Khelaifi said as thousands of fans gathered outside the stadium to welcome their new hero.
"It will be very exciting for our fans and fans worldwide. It is amazing what we have tried to achieve.
“We have a big ambition, a football project. We are very proud of where we are today. There is no secret this agreement is with this best player in the world."
Al-Khelaifi added: "There was a great desire on both sides to make this happen.
"This is just the start as the hard work will start now, on the pitch and off the pitch, but most important the person next to me has won a lot of trophies and I'm sure he will bring a lot more trophies to this club."