The 62-year-old Italian takes over from Fernando Santos after his contract expired following the World Cup, where he guided Greece to the last 16.
Ranieri has been handed a two-year deal and his main focus will now be steering Greece to Euro 2016.
"Claudio Ranieri signed a two-year contract with the Greek Football Federation and is the new coach of the national team," read a statement on the federation's website.
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"The Italian coach, with service at many major European clubs, is expected to lead our group to new successes with Euro 2016 on the horizon."
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