A Thai court has ruled Prime Minister Yingluck Shinawatra must step down over abuse of power charges.
The Constitutional Court ruled Ms Yingluck acted illegally when she transferred her national security head, the BBC reported.
The court also ruled some cabinet ministers involved in the transfer must also step down.
The ruling follows months of political deadlock. Anti-government protesters have been trying to oust Ms Yingluck since November 2013.
The move is likely to trigger protests by supporters of the government, which remains popular in rural areas.
Ms Yingluck had been accused of improperly transferring Thawil Pliensri, her national security chief appointed by the opposition-led administration, in 2011.
Appearing court on Tuesday, she had rejected the suggestion that her party had benefited from the move - but the court ruled against her.
"The prime minister's status has ended, Yingluck can no longer stay in her position acting as caretaker prime minister," a judge said in a statement.
The cabinet has decided Commerce Minister Niwatthamrong Boonsongphaisan will take over as prime minister.
A new election is planned for July.