Official results show the party took 31 of the 53 available seats in the country's National Assembly.
A coalition of seven parties that supported Mr Barrow during last year's presidential election has collapsed, with candidates from each now competing against each other.
24 candidates are contesting the election on the ticket of the National Reconciliation Party (NRP), the People's Democratic Organisation for Independence and Socialism (PDOIS) has 22 candidates, while 41 people are contesting the election as independent candidates.
Five seats are to be appointed by President Adama Barrow, totalling 58 spots in the small west African nation's parliament.
The vote was the first time Gambians had gone to the polls since President Yahya Jammeh stepped down in January after 22 years as head of state.
The president had initially said the opposition coalition was a "family" and would run again as a group in the legislative poll, but internal tensions broke apart the agreement.
"The only way Gambians can consolidate our newfound democracy is for people to ensure they elect competent individuals that will represent them in parliament and help in making the government's reform agenda a reality", said Fatou Suwareh, who was waiting in line to vote on the outskirts of Banjul.
Iran's Aseman Airlines Signs Up to Buy at Least 30 Boeing Jets
Asghar Fakhrieh Kashan, a deputy transportation minister, later said Iran would cut the number of Airbus planes to 112. Tehran slapped sanctions on 15 USA companies last month, in retaliation for American sanctions announced in February.
"We just hope that the voter turnout increases", said Manneh Sallah, vice-chairman of the electoral commission.
Jawara, who led protests previous year and said she had been subjected to torture by the now-defunct National Intelligence Agency, said she was confident about a victory in her constituency, which had been a stronghold of Jammeh's ruling party for the past two decades.
Alagie Bubacar Jallow, an unemployed hotel worker, said his town had always been ignored by the Jammeh regime because it was seen as an opposition stronghold.
"I'm not anxious about any party but I'm also not underrating any party", he added.
"As we voted for our candidates and they're the majority our suffering has come to an end", she said. He has pledged to carry out political, security and media reforms.
The results will be crucial for new President Adama Barrow, who will need his party to gain a majority in parliament in order to implement numerous policies he promised during his campaign.
The autocrat caused weeks of political impasse by refusing to accept the result of the December 2016 presidential election, which saw him lose power to Barrow. "What I am seeing is openness of the democratic process".
- Is the sky blue? Depends on what Donald Trump says
- Hyperloop One Picks 11 Proposed US Routes, Completes Test Track
- Girl found living with monkeys in Indian forest
- TASER changes name in shift to software, services for police
- The first drop test for the Galaxy S8 confirms your fears
- US, Russia Trade Claims About Who Used Chem Weapons in Syria
- Alabama Ethics Commission expected to hear Bentley case on Wednesday
- Demi Lovato: James Corden is the best damn diva
- Facebook launches resource to help spot misleading news
- Richard goes 8 innings, Padres beat Dodgers 4-0