Armenian President Armen Sarkissian resigned on Sunday, citing his inability to "influence" the political life of his country.
"The President does not have the necessary tools to influence the radical processes of domestic and foreign policy in these difficult times for the country and the nation," Sarkissian said in a statement posted on his official website.
The role of Armenia's president is largely ceremonial with the prime minister holding political power.
It comes as the president is at the centre of a political crisis following an outbreak of fighting between Armenia and neighbour Azerbaijan over control of the Nagorno-Karabakh region.
More than 6,500 people were killed in the six weeks of fighting, which ended in a Russian-brokered ceasefire agreement, granting Azerbaijan part of the enclave and surrounding areas.
Sarkissian and Pashinian disagreed on the decision to dismiss the army chief of staff in the aftermath of the conflict between the two former Soviet republics.
"At this difficult time for our state, when national unity is needed, the presidential institution should not be the target of gossip and conspiracy theories, thus diverting public attention from the most important issues," Sarkissian's statement continued.
Sarkissian was born in 1953 in Yerevan and was Prime Minister from 1996 to 1997 before being elected President in March 2018.
The Armenian economy has been struggling since the collapse of the Soviet Union in 1991.