[2] In early 2021, a handwritten letter was made public by Mikayel Minasyan, son-in-law of former president Serzh Sargsyan, wherein Mirzoyan agrees to be an agent for Armenia's National Security Service (NSS).

Notably, on 11 April 2018, he lit smoke flares during a speech in the National Assembly to call attention to the planned protests, which eventually did result in Sargsyan's resignation.

In January 2019 Mirzoyan was elected President of the National Assembly of Armenia, a position he held until August 2021.

On the morning of 10 November 2020, protesters seized the parliament building and pulled Mirzoyan from a car, demanding to know the whereabouts of Prime Minister Nikol Pashinyan, who announced a peace treaty with Azerbaijan just hours earlier to end the Nagorno-Karabakh War.

[8][9] In the presence of his child, Mirzoyan was beaten by a mob and was later taken to hospital, where he underwent surgery and was said to be in a good condition.