By Bond Robertson 
The 47-year-old lawyer became Estonia's first female prime minister in 2021. She is now leaving the post to lead the European Union's foreign policy for the next five years.
She refers to the job as a huge responsibility at a time of great geopolitical tension.
– War in Europe, and increasing instability in our neighborhood and globally are the biggest challenges facing Europe's foreign policy, Callas wrote on social media on Thursday evening.
She is the daughter of former Estonian Prime Minister and EU Commissioner Siim Kallas. In 2011, she followed in her father's political footsteps and was elected to the Estonian Parliament for the Liberal Reform Party founded by her father.
Great effect
She then travelled to the European Parliament, where she quickly gained a reputation as one of the most influential politicians in the parliament, despite the fact that tiny Estonia has a population of just 1.3 million.
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In 2018, she returned to Estonian politics as leader of the Reform Party, before being elected Prime Minister in 2021.
Callas has distinguished himself as a sharp critic of Russia and President Vladimir Putin. She was equally clear in her support for Ukraine.
Great support for Ukraine
Estonia is now among Ukraine's most generous donors, with support equivalent to more than 1 percent of GDP, according to Agence France-Presse.
“If Russian aggression succeeds in Ukraine, it will be an invitation to use it elsewhere,” Kallas said.
Estonia is bordered by Russia to the east.
Last fall, there was a storm around Kalas when Estonian media revealed that her husband, Arvo Halik, was part owner of a logistics company that continued to do business in Russia after the invasion of Ukraine.