The broadcaster confirmed he had received a positive test result last night, Stuff reports.
He says he is now feeling better and expects to recover completely soon.
He first revealed he was experiencing symptoms consistent with Covid-19 in a column this week for a business news website.
The veteran journalist also said his son had tested positive for the virus.
"A few days ago, I woke up but my body refused to move in any direction. I had a headache, my body was aching like something would break if I moved suddenly, and I had a frog in my throat," Garner wrote in a column for NBR.
"The next day I was close to being okay, so texted the ex-wife to organise picking up our son Buster for the afternoon. He's asleep, sick, she said. It then made sense," Garner wrote.
"Everything he was suffering from pointed towards Covid-19. So, we got him tested. Results confirmed Covid. My results are pending but, at the time of writing, all roads appear to lead to Covid-19. I can't taste anything, I'm sweating, I'm feeling hot."
Garner, who is double-vaccinated, said his 11-year-old son wasn't old enough to get the vaccine, and he urged people to have the jab.
"Get vaccinated. You're a mug for not doing it," Garner wrote.
