The retired athlete was tracked down by police in Queensland on Thursday evening.
Hours earlier he had been reported missing by his family , who said he needed "urgent help".
Hackett told police he 'doesn't want anything to do with his family .
The gold medalist in the 1500m in Sydney and Athens was arrested on Tuesday.
Hackett, who has had problems with drugs and alcohol away from the pool, has since been embroiled in a public slanging match with his parents and brother Craig.
On Thursday, Grant's father Nev Hackett said he had reported his son missing to police and said he is concerned for his welfare.
"He's definitely a missing person. He's mentally disturbed and needs urgent help... If anybody has seen him contact the media or the police or the Hackett family," Mr Hackett told local media.
"Grant, let us know where you are. We love you and we want to help you.
"He left a hotel at the Gold Coast at 7.30 this morning, very depressed and not in a good condition.
"We're extremely worried about him.
"His doctor can't find him, he hasn't kept an appointment with his lawyer."
On Wednesday, Grant posted a selfie to Instagram claiming his brother Craig - also a talented athlete - had beaten him.
"My brother comments to the media..." Grant wrote.
"But does anyone know he beat the sh** out of me.
"Everyone knows he is an angry man."
The claims emerged a day after Craig spoke publicly to the media about Grant 's arrest.
His family claims Grant had been drinking heavily and "had a mental breakdown", in the latest meltdown in his fall from grace.
Craig had spoken of how Grant had “the world at his feet” but was at the point where “we don’t know what’s going to happen - it doesn't look encouraging.”
“He’s a danger to himself," Craig had said.
"He’s a danger to the community. The Grant Hackett that Australia fell in love with, they can still have that affection towards him. This is not Grant Hackett.
“This is a completely different person. I don’t know this person, my mum and dad don’t know this person.
"He’s there in body, but he’s not there in mind, soul or spirit.”
The family had reported a domestic violence incident after Grant had allegedly flown into a rage.
But Grant was released by police without charge several hours later.
His father Nev reportedly said: "He's been receiving treatment from a doctor. He's big and powerful when he's not happy.
"We decided he needed some treatment but there was no way he was going to go and get treatment this morning, so we called the police."
Grant's fall from grace includes incidents including an alleged assault on a plane, stints in rehab after reports of a sleeping pill addiction and a marriage breakdown - including shocking reports of him trashing their family home.