A jail term keeping an unremorseful Sydney extremist incarcerated until at least 2044 is undoubtedly severe but justified, NSW's most senior judge says.
Milad Atai, 24, was jailed in 2018 for a maximum of 38 years for helping arm a 15-year-old who later murdered NSW Police accountant Curtis Cheng in Parramatta in October 2015.
Despite smiling at the time, Atai appealed - arguing the judge had disregarded his youth, imposed excessive and disproportionate terms and made an error when setting the total term.
It didn't fly with the NSW Court of Criminal Appeal, which on Monday unanimously dismissed the appeal.
Chief Justice Tom Bathurst said NSW and Victorian courts had consistently found the weight youth plays in lowering a sentence needs to be moderated in terrorist cases where the offender participates in planning and carrying out acts of extreme violence.
Atai had also affirmed his extremist beliefs and has ultimately demonstrated no remorse for the crimes he committed, he said.
Ahead of his sentencing, the terrorist said he supported the Taliban and Al-Nusra Front, a prescribed terrorist organisation, and withdrew an apology to the Cheng family.
"His prospects of rehabilitation are guarded, if not poor," the chief justice said.
He rejected comparisons to the 20-year term handed to Sulayman Khalid for a 2014 plot to gun down police officers and attack government buildings, saying no particular target was identified, much less attacked.
"Although the ultimate sentence is undoubtedly severe, it seems to me that having regard to the total criminality involved, (Atai's) lack of remorse associated with his ongoing commitment to Islamic State justified, the total sentence of 38 years which was imposed," Chief Justice Bathurst said.
"In my opinion it could not be said to be unreasonable or plainly unjust."
The reasons were supported by Justices Natalie Adams and Derek Price.
Atai will be 48 when he becomes eligible for parole in September 2044.