The parents of Sebastian Selo say they are now hopeful for a better future for their son.
Sebastian, from south London, had a rare tumour-like growth which used to trigger painful epileptic seizures almost every day.
However, the five-hour operation at the Royal Children's Hospital in Melbourne, the seizures have eased.
This, in turn could help improve his autistic behaviour, which has severely impeded his development.
His mother Anna told a news conference: "Sebastian's much more with it - the whole demeanour is different. When he requests something, he looks at us."
Doctors warn that it is early days yet, but they say there is a 50-70% chance that Sebastian will be completely seizure-free in future.
The tissue growth in the brain, known as a hypothalamic hamartoma (HH), is a ball of tissue the size of a grape in what should be an empty cavity.
As well as triggering seizures, it had affected Sebastian's appetite, emotions and behaviour, and also his ability to speak and walk.
His father Louie said it was "fantastic" that the seizures had stopped - but also hoped he could recover in other ways.
"If he can start to benefit and learn and achieve some of his potential, that would be great, that would be fantastic," he said.
His mother Annie said: "We believe in Sebastian. We believe that behind the illness, behind the torment of the seizures...there is a child who's intelligent, there's a child who can be creative, there's a human being."
Brain incisions
Sebastian's family had raised £25,000 to pay for the flight and medical treatment.
During the operation, doctors made incisions from the top of the brain instead of the base, to avoid nerves and arteries, and to lessen the danger of a stroke occurring.
The hospital leads the field in carrying out the procedure.
Children have flown to Australia from all over the world for the procedure, which has been performed 18 times over the last four years.
Eleven of them are now completely free of seizures, five improved "dramatically", and two showed moderate improvement
Sebastian will stay in Melbourne for a month for observation and further tests after the operation.