Mezey to leave Hungarian champions Videoton
Fehervar were crowned champions last Wednesday when they beat Kaposvar 3-1 at home and took an unassailable eight-point lead over Paks two rounds before the end of the season.
Mezey, who worked for Videoton for 18 months as a sports director before becoming manager in 2009, said his contract was running out and the club did not want to extend it.
"I am proud of what I have done here, I have accomplished the goals the club set for us. I am a bit disappointed about the decision but fully accepted it," Mezey, 69, was quoted as saying on the club website.
Sousa's arrival will be made official at a news conference on May 24. The former Portuguese international has managed England's Queen's Park Rangers and Leicester, and Welsh club Swansea City.
Mezey will remain in charge of Videoton until the end of the campaign and could finish with the double as the club play in the Hungarian Cup final against Kecskemet on Tuesday.