The goalkeeper was frozen out for 12 months over a contract dispute with Cagliari, having gone from representing the Azzurri in the World Cup to sitting in the stands of the Stadio Sant'Elia.
"I am happy to have arrived here," he smiled at the start of pre-season training with Lazio.
"I am very motivated and the President immediately convinced me to accept this proposal, especially as the side is already very competitive. I can't wait to get started."
It remains to be seen how long it'll take Marchetti to rediscover his form after a year on the sidelines.
"I certainly haven't forgotten how to save a shot, so I'm absolutely relaxed.
"The hunger to get back into the Nazionale is so strong. Right now I want to do well here, then if that leads to Cesare Prandelli giving me a call, that's even better."