The capital side have made another surprise signing with the addition of another talent to their ranks, and the Dutchman is evidently looking forward to life in Portugal
The 27-year-old has signed a three-year contract with the Portuguese side after the two clubs concurred on a €850,000 deal.
Schaars, who had only one more year on his AZ contract, had been strongly tipped to join PSV, but Sporting moved in quickly to secure their second Dutch player of the summer, following the arrival of Ricky van Wolfswinkel from Utrecht.
Sporting have also signed Peruvian duo Andre Carrillo and Alberto Rodriguez, while Domingos Paciencia was appointed as the club's new coach.
At his official presentation, Schaars said: "I am looking forward to playing. I have come to a great club with a great history. I will fight to be champion."
Earlier on Thursday, the father of Arsenal striker Nicklas Bendtner revealed Sporting Lisbon were plotting a move for the Danish player.