The Harmony party could win 25 mandates in the 100-seat Saeima. The estimate was made by the LETA news agency based on returns from 994 polling stations.
A total of 1,078 polling places opened across the Baltic nation on Saturday. Thirteen parties are vying for seats. Social Democrats were leading the race with almost 20 percent of the vote.
The KPV LV is likely to get 16 seats, followed by the New Conservative Party with 15 seats. The All For Latvia national alliance and Development/For! may each claim 13 seats.
The Greens and Farmers Union is set to win 11 seats, while the New Unity brings up the rear with predicted seven seats. The rest of the parties are not likely to clear the 5-percent threshold.
The Socialist party, commonly known as Harmony, received nearly 20 percent of the vote after ballots from 575 polling stations were counted.
The second-placed KPV LV got 14.35 percent of votes, followed by the New Conservative Party with 12.73 percent.
The Greens and Farmers Union gained 12.55 percent of the vote. The All For Latvia national alliance came fifth with 10.4 percent.
The For! received 9.76 percent, and New Unity cleared the 5-percent threshold with 6.37 percent of votes.
Latvians went to the polls on Saturday to elect all members of the 100-seat Saeima, the nation's unicameral parliament. There are 16 parties running for the seats.