Hoddle Street killer Julian Knight, one of Australia's most notorious mass murderers, has lost a last ditch High Court fight to overturn laws specifically designed to keep him in prison indefinitely.

Knight killed seven people in Melbourne's Hoddle Street in a shooting spree in 1987, injuring 19 others.

The laws have prevented Knight from applying for parole. ( AAP: Julian Smith, file photo )

He was later sentenced to life in prison, with a 27-year non-parole period.

Just before the period expired in 2014, the Victorian Government introduced laws naming Knight, and preventing him from seeking parole unless he was seriously incapacitated or in imminent danger of dying.

But Knight challenged the laws, arguing they interfered with the independence of the court which imposed the non-parole period.

The High Court today found the laws keeping Knight in jail did not interfere with the sentence imposed by Victoria's Supreme Court, as the decision on parole fell outside the court's powers.

"Whether or not Mr Knight would be released on parole at the expiration of the minimum term was simply outside the scope of the exercise of judicial power constituted by imposition of the sentences," the court found.

When the laws were introduced in 2014, Victoria's then-premier Denis Napthine said Knight "deserved to rot in jail".

Knight recently wrote an open letter of apology to his victims, the police and the public, in which he described his crimes as "despicable, cowardly and senseless".

"Thirty years have passed since the Hoddle Street shootings and I am far from the immature, disturbed and desperate teenager who committed them," he wrote.

"If I had been granted parole back in 2014 I would have very quickly faded into obscurity."