Laxalt has joined on loan with option to buy at the end of the season for €12m.
“I come to Toro with great enthusiasm, ready to put myself immediately at the disposal of the Coach and my teammates," Laxalt told the club website.
“I will reunite with Coach Walter Mazzarri, who I knew from my time at Inter, and many lads who are friends more than simply former teammates. Their support will help me settle in quickly into this new environment.
“I thank the club for putting its faith in me and salute all the Toro fans: running and playing football is even more wonderful when you do it in front of a crowd that supports you and makes you feel important."