Verratti has long been considered a top target for the Catalan giants and the Italy international's agent Donato Di Campli described him as a "prisoner" in Paris.
But after Verratti apologised to PSG and dropped Di Campli, becoming a client of Mino Raiola instead, the midfielder committed his future to the club.
"It was a bit difficult," said Verratti. "With my former agent, we were and still are friends, but some things did not please me and I made the choice to change.
"I had a discussion with the club, because there were things that were wrong or that I did not understand.
"Now I am happy to be part of this project, one of the most ambitious in Europe, and a player like [Julian] Draxler, who is one of the best players I've ever played with, could be on the bench."
Verratti is on international duty with Italy, who face Spain in a World Cup qualifier at the Santiago Bernabeu in Madrid on Saturday.