The 6ft 8in second rower has played 16 times for Argentina since making his debut against Scotland in June 2010.
He played three matches for Argentina at the 2011 World Cup and has appeared four times in this year's Rugby Championship.
The 26-year-old - a student of medicine - moved to Leinster in the summer of 2010 but left later in the season to ply his trade for the Argentine side Pampas XV, who were taking part in the Vodacom Cup.
Dean Ryan said: "We're looking for people who want to operate here and want to lift the tempo and play at a high level.
"Mariano fits into that category and will add to our side as we build for the future."
Warriors can also announce that winger Dean Hammond has signed a contract to stay at Warriors after impressing during a trial at the club.
The 21-year-old, who featured for South Africa in the Under 20 World Championship in 2012, has impressed during Aviva A League matches against Gloucester United and Northampton Wanderers since arriving at Sixways.
Ryan added: "I really like him. He played really well in the A League games. He's the sort of youngster that I want to be able to generate more of. We see him as a development project.
"He's got ability. And to have presence of personality to go to the other side of the world on your own and put yourself out there is quite strong."