Victorian party members made the decision at a conference in Ballarat on Saturday attended by state and federal Nationals MPs.
Senior federal Victorian MP Bridget McKenzie said it was a historic day for the state party.
The senator posted a photo of herself standing alongside federal Nationals Leader David Littleproud, federal coalition Indigenous Australians spokeswoman Jacinta Nampijinpa Price and Victorian Nationals Leader and state opposition Aboriginal affairs spokesman Peter Walsh after the vote.
“The conference voted effectively unanimously to oppose the voice because there is just not enough information available,” Mr Walsh told Sky News.
Later this year, Australians will vote on enshrining an Indigenous voice to parliament in the Constitution.
The federal Nationals announced their decision to oppose the voice last year, saying it would do nothing to help Indigenous people in their communities.
“I absolutely believe in recognition, reconciliation and importantly better outcomes for Aboriginal and Torres Strait Islanders, but Albanese’s Voice proposal will divide Australians along the lines of race and will have hidden consequences,” Senator McKenzie said in a statement.
“I am immensely proud of our Victorian Nationals who have today boldly stood for a united Australia.”
As National Reconciliation Week gets underway on Saturday CLP MP Senator Price said the debate on the voice needed to be respectful and shouldn’t target individuals.
“Victorians who do not support the Voice can have faith in The Nationals who know it is not racist to oppose it,” she said.
“This proposal is dangerous. It is risky. It is divisive and it will not improve the life of a single person who is living in disadvantage.”
The theme of this year’s National Reconciliation Week is ‘Be A Voice For Generations’, which spotlights those who fought for justice and those working to tackle the unfinished business of reconciliation, including the voice to parliament.
National Reconciliation Week runs until June 3 and is organised by the not-for-profit Reconciliation Australia, which is responsible for building and promoting reconciliation between Aboriginal and Torres Strait Islander peoples and non-Indigenous Australians.