Shortly afterwards, outgoing leader Alexis Tsipras welcomed her at the PM`s office for the handover ceremony.
"I am very happy to welcome the first female Prime Minister in the history of the Hellenic Republic. It is a significant step. I am certain you and the transitional government will perform your duties in an excellent manner in a crucial period for the country," Tsipras said.
Thanou has become a familiar face to Greek citizens in recent years appearing on TV channels as President of the Association of Greek Judges and Prosecutors strongly criticizing austerity measures and urging for a solution that will respect Greek people`s dignity.
She said of her duties as interim Prime Minister: "The main task of caretaker governments is the conduction of the elections with transparency."
"However, under the current circumstances, I think that this interim government will be called to face also other major issues, such as immigration," Thanou noted.
Her appointment came after the three largest parties in the current parliament failed to form a government and avoid the polls following the resignation of Tsipras` government a week ago.
Friday also marks the expected announcement of election day - which will most likely take place on Sept. 20, according to Greek state sources - as well as the dissolution of the parliament.
On the way to the fifth general elections in the debt-laden country in six years, and the second this year, Tsipras has stated that he forced the fresh polls because he felt it was his moral duty to request a fresh mandate from Greek citizens to move forward.
In the Jan. 25 national polls, Tsipras` Syriza party came to power pledging to reverse the harsh austerity policies of the past five years and implement an alternative strategy to overcome the debt crisis.
Following lengthy negotiations with Greece`s international lenders, Tsipras` government reached a new bailout deal this summer, the third since 2010, to avert a looming bankruptcy and a Grexit.
The Leftist leader has repeatedly defended since July his decision to accept a new, painful cash-for-reforms deal for the next three years as the only credible solution to keep Greece afloat and on the path to economic recovery.
In his statements over the past week, he requested a new, clear mandate from Greek people to implement the program.
His goal, according to political analysts in Athens, was to secure absolute parliamentary majority and form a stronger, more stable government to implement the controversial measures.
In the outgoing 300-member strong parliament, Syriza held 149 seats and formed a coalition government with the Independent Greeks party.
However, Tsipras` "honest compromise" with lenders was rejected by some of Syriza`s members as a "humiliating and catastrophic roadmap" for the country.
Following a revolt within Syriza, a new anti-bailout party led by one of Tsipras` former ministers was created last week. Pollsters in Athens expected the Popular Unity formed by Panagiotis Lafazanis would "steal" crucial votes from Syriza.
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