President Toomas Hendrik Ilves signed the decision to appoint Keit Pentus-Rosimannus as the new Minister of Foreign Affairs and MP Mati Raidma to replace her as the Minister of the Environment.
Pentus-Rosimannus, who was until now the Environment Minister, will replace Urmas Paet, who, after a u-turn, decided to take up a seat in the European Parliament.
Raidma swore an oath in front of Parliament, which Pentus-Rosimannus had already done.
Raidma has been a Reform Party MP since 2007, advising the prime minister and heading the Rescue Board before that.
Pentus-Rosimannus headed the Prime Minister's office before becoming a member of Parliament in 2007. She served as the Environment Minister from 2011.
The change means the Reform Party has swapped out or shifted three ministries in two weeks as Maris Lauri became the new Finance Minister at the beginning of the month, following the resignation of Jürgen Ligi.
The national elections are just 104 days away.