The Serie A outfit has strengthened its midfield with the Brazil Under-20 international ahead of the 2013-14 campaign.
The 20-year-old had long been linked with a move to the Serie A side and has now signed a five-year deal with the Biancocelesti to complete his transfer.
Anderson is a product of the Santos youth academy and made his official first team debut for the Brazilian giant in Oct. 2010.
The midfielder had since developed into a key player at Santos, attracting the interest of a number of European sides in the process.
Lazio initially struck a deal with Santos to sign Anderson in January, but the move then fell through following complications over the necessary paperwork.
Anderson will now continue his career in the Italian capital after all, though, as he joins compatriots Hernanes, Ederson and Andre Dias.