The 34-year-old has become the first player in 36 years to cross the Roman divide, signing for Lazio from arch rivals Roma.
The former Chelsea player has signed a two-year deal and will link up with former Blues boss Maurizio Sarri again.
Roma released Pedro from his current contract, with manager Jose Mourinho deeming him surplus to requirements.
Pedro was a regular starter in Serie A under Mourinho’s predecessor, Paulo Fonseca, making 40 appearances in all competitions, with six goals and seven assists.
The controversial move is softened somewhat by Lazio not having to pay for Pedro, with him signing on a free transfer.
The last player to move between the sides was goalkeeper Astutillo Malgioglio in 1985, and prior to that defender Carlo Perrone in 1981.
Aleksandar Kolarov, Sinisa Mihajlovic, Diego Fuser, Angelo Peruzzi and Roberto Muzzi also played for both clubs, but did not move directly between them.