Tuhirangi-Thomas Tahiata, then 28, was sentenced in February 2020 after a Brisbane Supreme Court jury found him guilty.
The decomposing bodies of Cory Breton, 28, and Iuliana Triscaru, 31, were found in a large metal box at Scrubby Creek, south of the city, on February 11, 2016.
They had been forced into the container at a home in Kingston 18 days earlier.
In sentencing, Justice Peter Davis said although Tahiata played no role in beating and restraining the pair, it was obvious he knew he was "driving them to their deaths".
Tahiata's appeal was subject to a hearing in October 2023 in which his barrister April Freeman claimed the jury had been influenced by inadmissible evidence.
Ms Freeman said during that hearing the trial's jury were told Tahiata had confessed to police while their interview video camera was switched off.
A police officer testified at the trial that Tahiata said: "I did it. I killed them. I murdered both of them".
The specific words Tahiata used during the confession were later ruled inadmissible as they were not an acceptable record under legislation governing Queensland Police conduct.
Ms Freeman said the quote from Tahiata was presented to jury members as a "pivotal moment" in the trial.
In a judgment handed down on Friday, Justice Peter Flanagan found that Tahiata's inadmissible confession was materially corroborated by other evidence that included CCTV footage linking him to the scene of the crime.
"It remains the fact that the appellant did receive a text which requested him to attend (the unit where the victims were detained), to which he agreed," Justice Flanagan said.
Throughout the trial, the court heard a dispute over drug debts resulted in Mr Breton and Ms Triscaru being bashed with a metal pole and forced into the toolbox by a group of Tahiata's schoolmates.
At sentencing, Justice Davis described the victims' deaths as horrendous.
"Most likely the two deceased were alive and screaming for their lives when they were placed in the creek," he said.
"It is haunting to imagine the moment that the toolbox slipped under the water, plunging the night into silence."
Tahiata, one of three men convicted over the murders, will have to serve at least 30 years behind bars.
He will not be eligible for parole until February 2046.
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