Contract: June 2015
A statement on the Italian club's official website confirmed the striker will be playing in Serie A after flying into Rome for his medicals.
Transfer details were not disclosed by Lazio, but reports suggest the club paid Panathinaikos a €6 million fee.
The former Liverpool man has signed a four-year contract worth €2.1m per annum.
Lazio president Claudio Lotito told the press: "We have great quality now and we hope to show this on the pitch.
"All the players have quality and Cisse is eager to do well on the field."
Cisse, 29, is now expected to join up with the rest of his new team-mates for their pre-season training camp in Auronzo di Cadore.
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