There were scenes of jubilation on Monday in the Armenian capital Yerevan after protests forced the resignation of Prime Minister Serzh Sargsyan.
Opposition supporters accused Mr Sargsyan, who was made prime minister last week after serving 10 years as president, of clinging to power.
"The street movement is against my tenure. I am fulfilling your demand," Mr Sargsyan said in a statement.
Former prime minister Karen Karapetyan has taken over as acting PM.
The announcement came soon after opposition leader Nikol Pashinyan was released from detention. Mr Pashinyan had been arrested on Sunday after he called for Mr Sargsyan's resignation during televised talks.
As well as Mr Pashinyan, two other opposition politicians and some 200 demonstrators were held.
In his statement published on his website, Mr Sargsyan said he was "addressing all citizens of the Republic of Armenia... for the last time as leader of the country."
"Nikol Pashinyan was right. I was wrong," he said. "The situation has several solutions, but I will not take any of them... I am leaving office of the country's leader, of prime minister."
His spokesman, Hovhannes Nikoghosyan, told the BBC that Mr Sargsyan was behaving responsibly and fulfilling the demands of the street movement which opposed his appointment as prime minister.
"I think his resignation is a clear demonstration of a democracy in force. It's not that every demonstration in every corner of the world leads to the resignation of the authorities," Mr Nikoghosyan said.
