However, the party is insisting a parliamentary inquiry be held into the South Australian election despite the victory.
One Nation's Chantelle Thomas had already been declared the winner of the seat of Narungga after the SA election in March, claiming it by a margin of just 58 votes.
But a new count was ordered for Friday after the SA Electoral Commission uncovered 81 ballot papers.
The uncounted votes were in three sealed boxes and had been returned to the commission.
The Narungga result remained unchanged after the newly discovered ballots were counted, with Ms Thomas extending her margin to claim the seat by 74 votes.
One Nation was happy with the result but backed calls for a review of the state election.
"One Nation welcomes today's outcome; however, we remain committed to establishing a parliamentary inquiry into the conduct of the South Australian election," a party spokesperson told AAP.
Of the 81 ballots counted on Friday in the presence of scrutineers, 46 went to Ms Thomas and 30 to Liberal candidate Tania Stock.
One ballot was rejected and four were deemed informal, the SA Electoral Commission said.
"Had the ballot papers been included in the original count and subsequent recount, the margin in favour of Chantelle Thomas One Nation would have increased from 58 to 74," Acting Electoral Commissioner Leah McLay said in a statement.
"I have therefore determined that the result in Narungga would not have differed had the ballots been included."
Ms Thomas was declared the winner of the Yorke Peninsula-based seat earlier in April, following a recount due to the tight voting margin.
The SA Electoral Commission was set to seek legal advice and petition the Court of Disputed Returns if the new count on Friday changed the election result.
Ms McLay on Thursday said the SA Electoral Commission would support any independent external review into the 2026 state poll.
One Nation officially has four lower house seats following the March 21 state election in a stunning result for the party.
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