Former Billabong chief executive Matthew Perrin has been found guilty of the fraud of millions of dollars by a jury in the District Court in Brisbane.

After a day-and-a-half of deliberation, the jury found Perrin, 44, forged his then-wife's signature on mortgage documents to get more than $13 million finance from the Commonwealth Bank.

He admitted signing his wife's name, but claimed he had her permission.

The former multi-millionaire surf wear boss committed the offences in 2008, after a series of failed investments left him facing financial ruin.

Perrin did not say anything when the verdict was delivered, but kissed his partner Belinda Otton, who was sobbing.

He was remanded in custody and is likely to be sentenced in the new year.

Ms Otton broke down in court after the verdict, and was visibly upset outside court.

The trial heard Perrin and his then-wife, Nicole Bricknell, netted about $60 million from their stake in Billabong when it was publicly floated in 2000, and lived in an $8 million Gold Coast mansion.

But their fortune evaporated after Perrin's investments in a Chinese supermarket franchise soured, leaving him owing tens of millions of dollars to creditors.

He was eventually declared bankrupt in 2009.

Perrin approached the bank for loans and credit extensions in 2008, faking his wife's signature to mortgage the family home, which was in her name.

Ms Bricknell disputed this, arguing she had never given him such authority.

Perrin's ex-wife Nicole Bricknell said the Commonwealth Bank documents were signed without her knowledge. ( AAP: Dan Peled )

Perrin's legal team claimed Ms Bricknell was going after their client "out of revenge and malice to see [him] in jail".

But Crown prosecutor Glenn Cash said Perrin had gone to considerable effort to provide the doctored documents to the bank, and his explanations for signing other people's names was "utterly unsatisfactory" and at its heart, a "total fabrication".

"The documents screamed dishonesty, and the defendant took a massive and dishonest risk in the hope it would all somehow work out," he said.

Mr Cash said while other high-stakes punts had paid off for Perrin in the past, this one did not.

"It failed catastrophically, and it failed fundamentally because the defendant acted dishonestly from the get-go."

Matthew Perrin faces a maximum 12 years in prison.