MVR party chief William Lara, who leads President Hugo Chavez's Fifth Republic Movement, said on Sunday his party would control 114 seats as a result of the vote, with the rest going to parties that supported the president.
"MVR managed to get 114 deputies elected and according to the figures we have, all 167 members of the National Assembly are supporters of the project written into the Bolivarian constitution," Lara said in a reference to Chavez allies.
The National Electoral Council has still to provide final results. But with just 114 MVR seats in the Congress, the pro-Chavez alliance would have more than the two-thirds it needs to press for what they call necessary reforms, such as allowing unlimited re-election to the presidency, which opponents fear will give even greater authority to the former army officer.
Most opposition groups abstained from voting on Sunday after accusing electoral authorities of favouring the populist leader and manipulating electronic voting machines, despite agreeing previously to participate in the election.
Chavez, a frequent critic of Washington, has accused US officials of orchestrating the boycott to trigger a political crisis. But he said the move included only a minority of candidates and could not invalidate the vote.
"These old parties, they are already dead -but they are still hanging on, resisting death"
"These old parties, they are already dead - but they are still hanging on, resisting death," Chavez said after casting his vote in Caracas. "Now they've accelerated their own demise."
The party chief, Lara, insisted that after 5 January, when the new legislature is inaugurated, Venezuela will still have a "multi-party National Assembly, which will include various civic groups and independent deputies".
Only 25% of about 12 million registered voters showed up as most of Venezuela's opposition parties, including Democratic Action and COPEI - which for decades alternated the presidency - stayed away from the polls, charging lack of transparency, according to election officials.
Jorge Rodriguez, president of the National Electoral Council, said the low turnout was caused by "torrential rains that have prevented voters from getting to polling places".
The election was mostly calm in Caracas. Officials had suggested "extremist groups" linked to Chavez foes were plotting violence to scuttle the vote, a charge opposition leaders say was just a distraction tactic.
Since Chavez won a referendum last year, his opponents have struggled to overcome divisions and distrust of the electoral council, which they charge manipulated voting machines to help Chavez defeat the 2004 recall vote. Observers said they found no vote-tampering in that referendum.