Australia's decision to hand Naval Group an $80 billion submarine contract without a backup plan left the nation "captured" by the French company.
Ron Finlay from the Naval Shipbuilding Advisory Board said the government had compromised its negotiating power by "down-selecting" to the French option in 2016.
Under questioning by Labor's Penny Wong at a Senate estimates hearing on Wednesday, Mr Finlay said naming the French defence giant without any alternatives had put Australia at a disadvantage.
"In my experience, many decades of negotiating major contracts, if you do not have an alternative of either going to bidder 'b' or cancelling the project, yes you are captured in a negotiation with few options," he said.
"And, that does increase the number of issues that can become a block to concluding the negotiations."
The government announced the selection of Naval Group - then known as DCNS - for the future submarines project in April 2016.
Australian Associated Press