The 31-year-old was voted the player of the 2011 Six Nations tournament, and has been capped 69 times.
Masi said of the move: "I am really excited and honoured to be joining such a great European club and I am hoping that I can add something to the club both on and off the field."
"Andrea is a versatile player with proven quality and he will be bringing some vital experience," Wasps director of rugby Dai Young added.
"We are always looking to add real international quality. I see him giving us great depth in our back-line."
Masi had also previously spent time at Viadana, Biarritz and Racing Metro.