Leaving F.C. Barcelona, Messi is set to join P.S.G. on a two-year contract that highlights the growing gap between soccer’s rich and its superrich.

Paris St.-Germain, the French soccer powerhouse bankrolled by the state of Qatar, has signed Lionel Messi, the Argentine star who is one of the best players of his or any generation.

The agreement, for two seasons plus an option year, comes days after Messi bid a tearful farewell to F.C. Barcelona, the club where he had spent his entire professional career. It concluded a brief and exclusive bidding war for Messi and added unmatched star power to the roster of P.S.G., a superteam that has become a fixture in the late stages of Europe’s Champions League, the world’s richest soccer competition.

In a news conference on Sunday, Messi broke down in tears as he confirmed what the club had announced last week: that Barcelona’s current financial crisis and the Spanish league’s cost-control rules made it impossible for him to sign a new contract. Yet even as he said goodbye, Messi seemed to be trying to soften the blow of his departure, for fans, for the club and also, it appeared, for himself.

“I did everything I could,” Messi said. “From my side, I did everything to stay. That is what I wanted.”