She will convene an extraordinary sitting of the parliament tomorrow to ask for a "mandate for the new government coalition" with the small conservative Fatherland "Isamaa" party and the opposition Social Democratic Party.
Kallas said in a statement that in order to form a new government, the current one needed to resign.
The three parties together will have a majority in the 101-seat Riigikogu legislature.
The deal means that Kallas, Estonia’s first female prime minister, will avoid governing a one-party minority government.
More about: Estonia