The 22-year-old defensive midfielder shone during Uruguay'sWorld Cup campaign, helping his nation to the quarter-finals before their exit against France on Friday afternoon.
It's great to see that Lucas Torreira has signed for the club.
He was warmly greeted by Unai Emery at London Colney as he arrived to complete the formalities, though he won't start training straight away as his season has only just drawn to a close.
Torreira featured in all five of Uruguay's World Cup matches and started in their last three, including a 3-0 win over fellow quarter-finalists Russian Federation and a 2-1 round-of-16 win over Portugal.
On his latest recruit, Emery said: "In Lucas Torreira, we have signed a young player who is a very bright talent in the game".
He will wear the No.11 shirt following Mesut Ozil's recent switch to the No.10 for the forthcoming season, but fans were a little confused by the choice.
France And Belgium World Cup Combined XI Is Pure Fire Emoji
With Eden Hazard alongside him (though Dries Mertens hasn't shown his Napoli form) Belgium have a formidable forward line. Tuesday's match will be the third time France and Belgium have met in a World Cup; France won both previous meetings.