The Australian Administrative Appeals Tribunal found that Doré - who was convicted for drug offending in 2018 - had a "low to negligible" risk of reoffending in Australia and it would be in the best interests of his daughter, now aged 4, if he were able to return.
It has now reinstated his visa.
Doré used to be a successful motorcycle salesman in Australia, earning $200,000 a year, until a relationship break-up and losing his job around the same time upended his life.
The tribunal said the combination of a financial shock in losing his income and the emotional difficulty of the relationship break-up led to a "psychological malaise" and depression.
Desperate to hold on to his mortgaged home, Doré began taking in boarders, who brought with them exposure to the drugs scene.
He soon became a daily user of methylamphetamine and, as his drug dependence became unaffordable, turned to dealing.
In February 2018, at the Brisbane Supreme Court, Doré was sentenced to three years and three months in prison for the possession of and trafficking in illicit drugs.
The prison sentence also triggered the cancellation of his visa under Section 501 which meant he would be deported once he had completed his sentence.
By that time, Doré had already undergone much of a rehabilitation programme and become the father of a baby girl to his former partner.
He began his battle to get his visa reinstated before he was deported.
"Four-plus years it took," he said.
He was able to join a group in prison who were given advice on how to appeal the decision, including what to say and not to say.
"I guess I was one of the lucky ones. When I joined the group we were given the information that the process was possible, where to find the application, who to send it to.
"We actually also got given the details of how to get in touch with an immigration lawyer."
Doré said the Australian authorities had tightened up and made the situation more difficult for deportees since he started the appeal.
"People are losing hope in the process. A lot of people are losing hope, actually," he said.
"I do a bit of work with a church here (in Auckland) ... and do quite a bit of work with the 501s. Anyone beating it is unheard of, really.
"Australia wanted us out, no matter what.
"On the surface they wanted it to look as though there was a legitimate process for an appeal to occur, but ... the process in itself was so difficult for everyone, really, that a lot of people can't see a way."
Doré said that 501s being deported to New Zealand arrived with "literally a backpack" and $300 given to them by Prisoners' Aid and Rehabilitation Society.
Doré said he was fortunate in that he had the support of his parents in New Zealand, where he chose to continue his appeal, rather than be held in an Australian immigration detention centre after release from prison.
The tribunal reviewed evidence that showed that since arriving back in New Zealand in July 2018, he has stayed drug-free and continued his rehabilitative process.
In 2020, he married his wife Emily, whom he met at a rehabilitation centre in Queensland before going to prison, and they now have a baby boy.
But it was the relationship with his daughter in Australia, that motivated Doré to continue to fight for a visa.
Doré said he was on good terms with his daughter's mother and had been able to stay in touch with the little girl.
Following his successful appeal, he has already began planning a visit, although he has no firm dates yet.
He had been allowed out of the rehabilitation centre to be present at her birth, and she had a photograph of Doré holding her.
Lately, she had been asking how he had been able to do that as she is so used to him only interacting with her through a video call on a phone.
Gavin and Emily Doré have both been accepted into postgraduate study at Auckland University, with a dream to create a rehabilitation programme for recovering addicts like themselves.
He is studying business and she is doing a postgraduate diploma in addiction and mental health.
Figures provided to Open Justice earlier this month showed 192 New Zealand deportees have applied to have their Section 501 deportations revoked since July 2020. Only 61 were successful.
More than 2500 people with New Zealand citizenship have been deported from Australia since 2015.
