In the past two days, all the parliamentary factions have either expressed support for Pashinyan's candidacy -which was announced on Monday-April 30 - as PM or have at least refused to nominate their own candidates for the prime minister's post.
After talks with Pashinyan on Sunday, the parliamentary leader of the Republican Party, Vahram Baghdasaryan, said the party would not "impede the election of the people's candidate" if all three opposition factions in parliament supported him.
Pashinyan met Sunday with Russian lawmakers, telling them his premiership would not threaten the South Caucasus country's close ties with Moscow.
Waving national flags and chanting Pashinyan's name, tens of thousands of people gathered in a square in the centre of Yerevan in the evening, according to an AFP reporter at the scene.
Protest leader Pashinian and his supporters can count on 47 votes in Parliament.
Sargsyan's Republican party holds a majority in parliament, which made him premier after he was termed out as president.
Drop off your drugs for Drug Take Back Day
Police encourage people to take advantage of these drug take-backs so unused medications don't end up in the wrong hands. The take back initiative only accepts pills and patches that are expired or unused; no needles or inhalers were taken.
The official representative of Russia's foreign ministry Maria Zakharova has said that relations with Armenia are "special" for Moscow.
The country's parliament, the National Assembly, is due to select a new Prime Minister on 1 May following the resignation of Serzh Sargsyan, amidst weeks of street protests against his rule.
The Republican Party has 58 seats in the National Assembly, the Tsarukyan faction controls 31 seats, the Yelk bloc of Pashinyan has 9 seats and the Armenian Revolutionary Federation has 7 seats.
The situation in Armenia is awkward for the Russian leadership.
Sargsyan's party has pledged it will not put forward a new candidate for prime minister to prevent an escalation of the political crisis.
Protest leader Pashinyan, a former journalist turned lawmaker who has been instrumental in organising the protests, has said he wants the job.