The creative midfielder has completed his transfer from Bologna to the Chinese club, where he will link up with his compatriot, World Cup-winning coach Marcello Lippi
The attacking midfielder had also been linked with clubs such as Inter and Juventus in the past few months but a transfer never materialised during the January window.
The 30-year-old has therefore opted to accept the Asian champions' offer and will link up with Guangzhou's Italian coach, Marcello Lippi.
"I am pleased to be able to start with my family this new adventure," Diamanti declared.
"I thank the whole club and especially the city of Bologna, which has made me feel important on and off the field."
Diamanti started his professional career with Prato and also wore the jerseys of Empoli, Florentia, AlbinoLeffe, Livorno, West Ham and Brescia before joining Bologna in the summer of 2011.
The creative attacker has been capped 17 times for Italy and was part of the squad that made it to the final at Euro 2012 two years ago.