The Spanish head coach has been very busy in the transfer market since taking over the reins from Arsene Wenger.
Torreira becomes the fourth addition to the Gunners squad since Emery’s appointment to further strengthen Wenger’s options in the middle of the park.
Arsenal are reported to have spent in the region of £26m on the Uruguay international, who impressed during their run to the World Cup quarter-finals.
Torreira, who has signed a long-term contract with the north London side, scored four times in 38 games for Sampdoria in Serie A last term.
Arsenal manager Emery delivered his verdict on Torreira following the addition of the South American holding midfielder.
“In Lucas Torreira, we have signed a young player who is a very bright talent in the game,” Emery told Arsenal’s website.
“A midfielder with great quality, I have enjoyed watching his performances for Sampdoria in the past two seasons, and we all saw him do very well for Uruguay in the World Cup.
“He is a young player already with good experience, but who wants to keep on growing. We welcome Lucas to Arsenal and look forward to him joining us soon for pre-season.”
Arsenal have already signed Switzerland veteran Stephan Lichtsteiner in a free transfer from Serie A giants Juventus in May.
The Gunners strengthen their options in goal with the £20m addition of Bayer Leverkusen goalkeeper Bernd Leno.
Arsenal raided the Bundesliga again to sign Sokratis Papastathopoulos to improve Emery’s options at centre-half.
The north London side finished in sixth spot in the Premier League table last season to miss out on a place in the Champions League for the second successive campaign.
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