Armenia's acting prime minister, Nikol Pashinyan, and his Civil Contract party won a parliamentary election with 53.92 percent of the vote, the Interfax news agency reported, citing the electoral commission.
Pashinyan had earlier claimed victory in Sunday's election based on preliminary results, with his party taking an early lead over its closest challenger, the Armenia Alliance, led by former President Robert Kocharyan.
"Not all the votes have been counted yet, but it is clear that we will have a convincing majority," Interfax quoted Pashinyan as saying earlier on Monday.
Kocharyan's bloc questioned the credibility of the preliminary results, the Sputnik media outlet reported.
Opinion polls had put the two parties neck and neck in a snap election the government called to try to end a political crisis that erupted after ethnic Armenian forces lost a six-week war against Azerbaijan last year and ceded territory in and around the Nagorno-Karabakh region.
Pashinyan has since been under pressure, with regular street protests demanding he step down over the terms of the peace agreement that ended the conflict. Under the deal, which was brokered by Russia, Azerbaijan regained control of territory it had lost during a war in the early 1990s.
Pashinyan himself described the agreement as a disaster, but said he had been compelled to sign it to prevent greater human and territorial losses.
Whoever forms a majority in the south Caucasus country's parliament gets to elect the prime minister, who is nominated by the president.
There were 319 reports of voting irregularities, RIA reported, citing the general prosecutor's office. The CEC said elections were largely in line with legal norms.
The Defence Ministry rejected allegations that servicemen were being forced to vote, saying conscripts voting in groups was systematically beneficial and that it was continuing to monitor the voting process.
Nationwide turnout stood at 49.4 percent when polls closed at 4pm(GMT), RIA reported.
Armenia, which hosts a Russian military base, is a close ally of Moscow, although Pashinyan, who came to power on the back of street protests and on an anti-corruption agenda in 2018, has had cooler relations with the Kremlin.
Turkey, which supported Azerbaijan in last year's conflict, will also be watching closely.
Kocharyan is a native of Nagorno-Karabakh. The enclave is internationally recognised as part of Azerbaijan but has long been claimed by its mainly ethnic Armenian population.
Kocharyan was president of Armenia from 1998 to 2008 and was accused of acting unlawfully when he introduced a state of emergency in March 2008 after a disputed election. At least 10 people were killed in the clashes that followed between police and protesters.
In a recent interview with Russia's RT TV channel, Kocharyan accused Armenia's leadership of inaction during last year's war and pledged to start negotiations on Nagorno-Karabakh's borders if he came to power.