Why were there protests?
In 2015, Armenians voted in a referendum to shift the country from a presidential to a parliamentary system, stripping powers from the president and giving them to the prime minister.
The vote was marred by allegations of ballot-rigging and claims Mr. Sargsyan wanted to switch office after his presidency ended merely.
The ex-president had formally stated he would "not aspire" to the prime ministerial position, but on Tuesday last week, the country's parliament officially confirmed Mr. Sargsyan in the post.
Protesters poured into the streets in the days beforehand to try to stop the parliament from passing the measure and clashed with police. On the day of the confirmation, Mr. Pashinyan said the demonstrations constituted a "non-violent velvet revolution".
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 the office of the country's leader, of prime minister.
Photo done by me today, using Iphone6
Source of the text: BBC News