Mirzoali Boltuyev, the Tajik central elections commission chairman, announced the ruling party's election victory.
"The People's Democratic Party of Tajikistan won 54 out of 63 seats in parliament, having won 70.6 per cent of the vote," he said.
The result is set to strengthen Emomali Rakhmon, the president, who has ruled the country for the last two decades.
The Islamic Revival Party, which came a distant second with 8.2 per cent of the vote, says it will challenge the result in the courts.
It has also threatened to take it supporters to the streets.
"If we get the permission to hold a protest, our party has the ability and the experience to conduct that," Muhiddin Kabiri, the party's leader, was quoted by The Associated Press as saying.
The election also saw three minor parties take six seats, while the 63rd and last seat will be filled after a run-off election on March 14.
Official turnout for the election was 90.3 per cent, according to election officials.
The OSCE said Tajikistan's laws may have led to unfairly balanced electoral commissions as well as a lack of fairness in voter registration, campaigning and election day procedures.
Tajikistan, which won independence from the Soviet Union in 1991, has co-operated with US-led military operations in its neighbour Afghanistan.