— S.S.Lazio (@OfficialSSLazio) August 27, 2020
Reina, 37, had a year remaining on his Milan contract but they released him to join Lazio.
The former Liverpool goalkeeper spent the second half of last season on loan at Aston Villa, making 12 appearances.
Valencia were keen on Reina to replace Jasper Cillessen but the club’s ongoing troubles meant no deal materialised.
Reina will provide competition for Albanian shot-stopper Thomas Strakosha at the Rome club.