De Vedia, 24, can also play full-back and was the leading tryscorer in Argentina's national competition last season.
He is yet to win a full Test cap but de Vedia played for Argentina A at this summer's Rainbow Cup in Portugal.
Saracens director of Rugby Alan Gaffney said: "Tomas is a very exciting player and we're delighted to have him as part of the squad.
"He's mainly a winger but can play anywhere in the back three and his record for both club and country prove that he is very good at finding the line.
"He is quick and is a very powerful player and we believe he will make an impact here. It's a great opportunity for him and also for us."