No details of the deal were announced by the club but Greek media reported that Everton will loan the 30-year-old player for six months at a cost of 3 million euros.
Mirallas played two seasons for Olympiakos (2010-2012) appearing in 52 matches, scoring 34 goals and leading the club to two league titles.
He was the leading scorer in the Greek Super League during the 2011-2012 season with 20 goals.
Mirallas has been at Everton since 2012 and has played in 151 matches scoring 29 goals.
He also played for French sides Saint-Etienne (2008-2010) and Lille (2004-2008).
Mirallas has 56 appearances with the Belgium national team scoring 10 goals.
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