She was the first female prime minister of Estonia, a role she held from 2021 until 2024, when she resigned in advance of her appointment as High Representative of the European Union for Foreign Affairs and Security Policy.

[15] During her period in Parliament, Kallas worked on the Digital Single Market strategy, energy, and consumer policies, and relations with Ukraine.

In particular, she defended the rights of small and medium-sized enterprises, maintaining that borders in the digital world hinder the emergence of innovative companies.

[22] At the end of her term, she was cited by Politico as one of the 40 most influential MEPs, and one of the most powerful women in Brussels, who was highlighted for her understanding of technological issues.

[28] Kallas won the leadership election held on 14 April 2018 and became the first female leader of a major political party in Estonia.

[35] Later in the year Kallas stated that Russian military pressure should not influence the decision of which countries can join the European Union or NATO, and she did not like U.S. President Biden's outreach to Putin.

[36] During the latter half of 2021, the global energy crisis disrupted the Estonian economy; businesses were forced to temporarily shut down, while the public requested government aid to pay for the high electricity and heating prices.

Kallas has been praised both in Estonia and internationally as a leading pro-Ukrainian voice in the war, with the New Statesman calling her "Europe's New Iron Lady".

[58] In September 2022, in the context of a plan by three other bordering nations to restrict Russian tourists, she said: "Travel to the European Union is a privilege, not a human right."

She added that it was "unacceptable that citizens of the aggressor state are able to freely travel in the EU, whilst at the same time people in Ukraine are being tortured and murdered.

"[59] In February 2023, Kallas was mentioned as a possible candidate to replace NATO Secretary-General Jens Stoltenberg following his expected retirement that same year.

[62][63][64] Following the election result, Kallas negotiated a coalition government with Estonia 200 and the Social Democratic Party, and her third cabinet was sworn in on 17 April.

The bill came into effect on 1 January 2024, making Estonia the first Baltic state and country formerly occupied by the Soviet Union to legalise same-sex marriage and adoption.

[69][70][71] Kallas is a transatlanticist[72] and was frequently named as a potential candidate to succeed Jens Stoltenberg as Secretary General of NATO, a role she has expressed interest in.

[84][85][86] Media reported that Kallas had provided an undeclared €350,000 loan to her husband shortly after visiting Metaprint as prime minister in January 2022.

[87][88] Stark Logistics seconded Kallas's claim that the company's dealings in Russia were to assist an Estonian client end their production in the country, and that their work did not contribute to the Russian economy in any way nor did it violate Estonian law, as Kallas's government had prohibited only state-owned companies from working with Russia.

[84][89] The Estonian media has separately reported that Metaprint sold €17 million worth of goods to Russia between the start of the invasion in February 2022 and November 2022.

[86][90][91] Hallik's business partner Martti Lemendik later admitted in the Estonian media that the company had sold over $32 million in goods on the Russian market between February 2022 and August 2023.

[95][96] Two opinion polls conducted by Norstat and Turu-uuringute AS showed that 57% and 69% of respondents, respectively, thought Kallas should resign due to the scandal.

In November 2024, she stated that the People's Republic of China must pay a "higher cost" for its support of the Russian invasion of Ukraine.

[105] On 1 December 2024, her first day in office as High Representative, Kallas visited Ukraine along with European Council President Antonio Costa and Enlargement Commissioner Marta Kos.

[106] Kallas expressed strong support for a Ukrainian victory, stating that "the European Union wants Ukraine to win this war".

[106] The trip was criticized by Slovak Prime Minister Robert Fico, who stated, without further elaboration, that Kallas and Costa had made statements that had not been agreed upon by EU bodies.

[107][108] On her first day in office, Kallas also warned the Georgian government not to use violence to suppress the ongoing protests against the ruling party's decision to postpone EU accession talks, threatening possible sanctions.