Before the election, some Latvians feared a strong result for Harmony and KPV could lead to them forming a government and bringing the Latvia's foreign policy closer to Putin's Russian Federation.
Members of the minority account for about 25 percent of Latvia's 2 million people, a legacy of almost 50 years of Soviet occupation that ended in 1991.
The pro-EU, pro-Nato liberal For Development/For! party came fourth in the vote with 12 per cent, beating parties from the current centre-right governing coalition including the right-wing National Alliance, which earned 11 percent. That, she said, is "good news for Latvia".
Pro-Russian "Harmony" party won the parliamentary elections in Latvia.
But with three hours to go, turnout was low at 39.06 percent, according to the election website.
The Baltic countries - Estonia, Latvia and Lithuania - have also noted with alarm a substantial increase in Russian military manoeuvrs in the region.
Some Latvians were optimistic about the results of the vote.
In the past, parties have formed pacts to keep Harmony out of government.
The result will lead to a more fragmented parliament of seven parties, of which six won between 10 and 20 percent support each.
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"The message that the voters have tried to send is that we're going to have some new faces in politics", Janis Ikstens, political scientist at Latvia University, told Reuters.
A pro-Russia party is poised to evict Latvia's western-friendly government and take power in the North Atlantic Treaty Organisation member state.
Casting his ballot in the eastern town of Rezekne, Aigars Karklins said the prospect of Harmony teaming up with populists was realistic.
Una Bergmane, a teaching fellow in global history at the London School of Economics, said it is unlikely the party will be able to team up with Prime Minister Maris Kucinskis' Union of Greens and Farmers, which polls suggest could come second.
The second place was taken by the party KPV, which gained 14.1%.
Kaimins was briefly detained over alleged corruption in June, but that does not appear to have bothered voters.
With 100 seats in total, any coalition model would need to control 51 seats to assure a simple majority in parliament.
The result means a confirmation of the European Union and North Atlantic Treaty Organisation member's role as a bulwark against Russian Federation in the increasingly hostile relationship between the West and President Vladimir Putin. Polling stations open on Saturday from 0500 GMT to 1700 GMT, with exit polls soon after and results expected early Sunday.