Dennis Rommedahl has moved to Olympiakos from Ajax on a two-year deal.
The club announced the free transfer on Wednesday after the 32-year-old ended his contract with the Dutch giants to move to Greece.
There are no official details of the deal but local media reports he will earn a salary of 850,000 euros a year plus bonuses.
Rommedahl enjoyed something of a renaissance in his career for Denmark during the World Cup, scoring one and making a goal in their 2-1 win over Cameroon in the group stage.
Olympiakos courted the Dane's services three years ago after he left Charlton but he chose to move to the Amsterdam ArenA instead.
"I know we must become champions once again and that's why I came," Rommedahl said.
"I know that it is the biggest club in Greece. I had other offers but my manager said the most serious was from Olympiakos."