The 44-year-old Spaniard joins from Sevilla, having guided the Spanish club to a third consecutive Europa League title. He replaces Laurent Blanc, who had parted company with PSG after three seasons in charge.
"It is with great pride that I agreed to become the Paris St Germain coach," Emery said in a statement. "The club has become one of the biggest in Europe over the past few seasons and I am both happy and honoured to be able to help realise its great ambitions."
The former Real Sociedad midfielder, who started his coaching career in 2004, coached Valencia from 2008 to 2012 before taking over at Sevilla in 2013.
Blanc departed officially on Monday. His future at PSG had appeared in jeopardy since club president Nasser al Khelaifi this month described the 2015-16 season as a failure because of the club's elimination from the Champions League by Manchester City.
PSG achieved their second successive domestic treble by winning Ligue 1, the French Cup and the League Cup, but Champions League progress stagnated as they lost in the quarter-finals for the fourth successive season.
Emery was tied with Sevilla until June 2017 but negotiated a release from his contract. Sevilla have appointed former Chile coach Jorge Sampaoli to replace him.
(Reporting by Patrick Vignal. Editing by Adrian Warner.)
