Emergency services rushed to the blaze in a unit in the Geelong suburb of Grovedale at 9.40pm and found two women in their 40s on the loungeroom floor.
The victims were named as Rachel and Clare Wallmeyer, who suffered from anorexia and detailed their battle on television in 2004.
Acting Insp Gary Coombes told the Geelong Advertiser the fire was being treated as non-suspicious.
He said the blaze was contained to the loungeroom and the cause was still being investigated.
Neighbours had raised the alarm after smelling smoke.
The pair have previously made suicide attempts and have said their only comfort was knowing they would die together.
“I think most people have accepted that we won’t live through this and we don’t want to live with it,” Rachel told the Geelong Advertiser in 2004.
But the two also had a volatile relationship, with Rachel accused of trying to murder her sister in 2010.
The women were carried out of the property by firefighters but one died at the scene and the other died a short time later as she was being flown to The Alfred hospital.
A report will be prepared for the Coroner.
Rachel Wallmeyer was once charged by police with the attempted murder of Clare.
It was alleged police were called to the apartment they shared in Camira Court in November 2010 when officers witnessed Rachel trying to throttle her twin sister and making threats.
She was also charged with recklessly causing injury and unlawful assault.
In an initial court case regarding the incident, it was heard a 12-month intervention order prohibiting Rachel physically assaulting her sister had been taken out by police at Geelong Magistrates’ Court two months earlier.
Rachel was granted bail and the matter adjourned for committal mention in February 2011.
The attempted murder charge was later withdrawn.
Clare and Rachel were well-known in Geelong.
The twins, who first had their story told in the Geelong Advertiser, talked of their struggle, said people started to notice them when they became anorexic at school.
Rachel said anorexia had made her into something.
“You take away anorexia and I am nothing, I don’t even know who I am,” Rachel said.