The 24-year-old has found game time at United extremely limited this season.
Now the Brazilian will have the chance to show his quality in Serie A with the historic capital club.
Lazio's official website stated: "Andreas Pereira has landed in Rome. At around 18:00, the Brazilian from Manchester United arrived at Ciampino airport, ready for a new adventure. He will undergo the usual medical examinations at the Paideia clinic tomorrow morning before becoming a new Lazio player."
Pereira will spend the season in Italy, while Lazio have an option to buy him during that period for a set fee.