"The House of Representatives voted unanimously to suspend the chief of government Fathi Bashagha and open an investigation against him," said the House spokesman Abdullah Bliheg after a closed-door meeting in Benghazi.
Deputies assigned the administration's finance minister, Oussama Hamad, to act as prime minister while the investigation takes place, Bliheg said.
The reasons for Bashagha's suspension were not immediately known.
Parliament, backed by military strongman Khalifa Haftar, had picked Fathi Bashagha in February, 2022 to lead a government to replace that of Prime Minister Abdulhamid Dbeibah, who sits in Tripoli.
In July, Bashagha had told AFP that he planned to take office in Tripoli "in the coming days."
The following month, local media and experts said he had failed in his second attempt to dislodge his rival by force, after clashes in Tripoli killed 32 people.
Since his failed attempts to force Dbeibah out, Bashagha has been based in the central city of Sirte.
Although he himself hails from Libya's west, he chose to strike alliances with the eastern-based figures Haftar, and parliamentary speaker Aguila Saleh, in the name of national reconciliation.
Libya fell into a decade of violence following the 2011 overthrow of dictator Moammar Kadhafi in a NATO-backed uprising.
Dbeibah was appointed as part of a United Nations-backed peace process to end more than a decade of violence that followed Kadhafi's overthrow and drew in foreign powers.
The eastern-backed administration argued Dbeibah had outlived his mandate, but he refused to hand over power before elections.
Elections scheduled for December 2021 were delayed over issues including their legal basis and the participation of controversial candidates. They have still not taken place.
