Balcazar, an 83-year-old former judge representing the leftist Peru Libre party, defeated three other candidates late on Wednesday with a majority of the 130-member legislature.
The revolving-door presidency in Peru reflects a political crisis fuelled by a lack of legislative majorities for leaders.
Lawmakers have frequently used a broad interpretation of a constitutional article regarding "permanent moral incapacity" to remove sitting presidents.
Balcazar, a retired judge with nearly 30 years of experience in the judiciary, was sworn in shortly after the vote by the president of the Congress, Fernando Rospigliosi.
He will govern for five months before handing over power to the winner of upcoming elections.
Peruvians will choose a new president and legislature on April 12.
If no presidential candidate receives more than 50 per cent of the vote, the two front-runners will advance to a runoff in June.
Balcazar's successor will confront a surge in murders and extortion that continues to devastate small business owners and the working class.
Various political groups are demanding firm guarantees for a transparent election.
Balcazar told reporters that he would ensure the upcoming elections were "unquestionable", that macroeconomic policies would remain unchanged, along with sound monetary policy "so that economic agents can work without concern", and that he would seek to refocus the fight against organised crime.
Congress had voted on Tuesday to remove conservative interim President Jose Jeri after four months in office.
The current Congress, which began its term in 2021, has now impeached three heads of state: Pedro Castillo, Dina Boluarte and Jeri.
In October 2025, Jeri was serving as president of Congress and was next in the line of succession to replace Boluarte, who had no vice presidents.
His own removal followed revelations regarding his undisclosed meetings with Chinese business owners, including a state contractor.
Jeri asserted he was merely co-ordinating a Peruvian-Chinese festival.
The Public Prosecutor's Office has launched two preliminary investigations into Jeri over allegations of illegal sponsorship of private interests and influence-peddling to the detriment of the state.
