“I think the time has come for me now,” the 32-year-old Mandzukic said in a letter circulated by the federation. "I gave my best for Croatia and I have contributed to the greatest success in Croatian football."
The Juventus player said that finishing in the runner-up spot in the 2018 World Cup had given him “new energy but also made this incredible decision easier”.
Mandzukic scored 33 goals for Croatia in 89 games and is ranked second only to the country’s Davor Suker.
French World Cup winner Nzonzi completes Roma transfer
France World Cup winner Steven Nzonzi completed his switch to Roma from Sevilla after signing a four-year deal with the Italian side.
Roma paid an initial fee of 30 million euros for the 29-year-old midfielder, who featured in five of France's seven games at the World Cup.
“I feel very happy to be here and to be a new Roma player,” Nzonzi told the club’s website.
"Steven is a footballer with a mix of physical and technical qualities that we think will really add to the players that we already have here," Roma sporting director Monchi said.
“With his arrival, we have even more quality and competition in midfield.”
Nzonzi joined Sevilla from English club Stoke in 2015 and was part of the team that beat Liverpool 3-1 in the Europa League final in 2016.
Roma finished third in Serie A last season and reached the semi-finals of the Champions League.