The Ivory Coast star has returned to the club he left for Monaco in 2006, five days after his agent confirmed he had completed a medical with an unnamed outfit in London.
Toure, who left Manchester City at the end of last season, says he turned down approaches from other teams in Europe, Asia and the United States in order to move back to Athens.
"It is an honour to be back at Olympiacos," he said via his official website. "When I left in 2006 I said I would come back and I am delighted to keep my word.
"I had offers from lots of clubs across Europe, Asia and the USA. Ultimately, I made my decision based on the special relationship I have with this incredible club.
"I am as hungry for success now as I was when I first arrived here many years ago and I cannot wait to help the club win the trophies the great fans of Olympiacos deserve.
"It is now time to let my football do the talking once again. Let's do this!"
Toure had been heavily linked with West Ham, with manager Manuel Pellegrini claiming the 35-year-old had wanted to move to London Stadium but was told the club had other priorities.
Toure won a league and cup double with Olympiacos in 2005-06, after joining from Metalurh Donetsk.
He would go on to enjoy a trophy laden career with Barcelona and Manchester City, winning two La Liga titles, three Premier League titles, a Champions League crown, FIFA club World Cup, three English League cups, an FA Cup and Copa del Rey during his time at the two clubs.
It is an honour to be back at @olympiacos_org !
When I left in 2006 I said I would come back and I am delighted to keep my word.
FULL STATEMENT here: https://www.officialyayatoure.com/general/yaya-returns-to-olympiacos/ …#YayaIsBack
