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.
Protesters chanted "Nikol, Nikol" in the streets on Monday, the 11th straight day of protests. They were joined by hundreds of uniformed soldiers, despite warnings from the defence ministry that any soldiers protesting would be harshly punished.
Mr Pashinyan congratulated the people on their "victory" following the resignation. "You have won, proud citizens of the Republic of Armenia. And no-one can seize this victory from you. I congratulate you, victorious people," he wrote on Facebook.
Mr Sargsyan had faced criticism in Armenia over his close ties to the Russian President, Vladimir Putin, who has also moved between roles as president and prime minister to maintain his grip on power.
Mr Putin's spokesman said on Monday that Moscow was closely watching events in Yerevan. "We are very attentively observing what is happening in Armenia," Dmitry Peskov told journalists, calling the country "extremely important" for Russia.
Asked if Russia would intervene, Mr Peskov said the matter was "exclusively an internal affair" and Russian action would be "absolutely inappropriate".
(Source: BBC)