Masi, 31, joins the Premiership club from the now defunct Italian side Aironi, and will fill the void left by Dominic Waldouck's departure to Northampton last week.
Masi has represented Italy in three World Cups, and was named the Six Nations 2011 Player of the Championship after scoring a try in the shock win over France, making him the first Italian to claim the award.
Prior to joining Aironi, Masi also had spells at Viadana, Biarritz and Racing Metro, and Wasps director of rugby Dai Young is delighted to have added the versatile three-quarter to his squad.
He said: "Andrea is a versatile player with proven quality and he will be bringing with him some vital experience from the highest level of the game.
"We are always looking to add real international quality to our squad and I see him as giving us great depth in our back-line."
Masi added: "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."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.