Lawmakers voted 59 to 42 to approve Pashinian as prime minister.
Ahead of the vote, Pashinian told the legislature he would fight corruption.
"There will be no privileged people in Armenia. Election results will no longer be falsified. No bribes will be distributed," he said.
"The leadership will not be a means to earn money. Corruption will be eradicated," Pashinyan said.
Thousands of jubilant Pashinian supporters celebrated in Republic Square and the streets of the capital Yerevan, having achieved a historic political change through the street mobilizations.
As it was reported earlier, the protest movement was sparked when Sargsyan took up the premiership early in April after he reached a term limit of 10 years as president. It was also fueled by anger over alleged corruption within the Republican Party elite. The party has ruled the country since the late 1990s.
The protesters were joined by opposition leader Nikol Pashinyan. Before the column goes the orchestra, the oppositionists beat the drums and play other instruments, carry the national flags of Armenia.
Pashinyan called for the resumption of mass actions on April 29, and on May 1 to go to the rally during the consideration of candidates for the post of prime minister in parliament.