Sevdet Ramdam Besin, 19, resident of Melbourne, in June pleaded guilty to planning the terror attack, EFE news reported.
Judge Michael Croucher condemned the Islamic State (IS) sympathiser to 10 years in prison, but he could be released on parole in seven and a half years, according to sources.
Croucher said it was unthinkable that a teenager could plot the murder of a policeman, plan to attack and behead him with a knife.
Besin, arrested a week before Anzac Day in 2015, discussed his plans with a young British national, who is currently serving a five-year sentence in prison after pleading guilty to inciting a terrorist attack during the celebrations.
During the process, the boys also discussed the possibility of painting a kangaroo with IS symbol, loading it with explosives and releasing it in a city.
Australia in recent years has registered an increase in adolescents and teenagers who, influenced by extremist Islamic movements, have carried out attacks in Australia or tried to leave the country to join the IS fight in the Middle East.
Australian authorities put the country on high alert in September 2014 and since then has tightened security and adopted a series of anti-terror laws to prevent attacks on its soil.
The current 'probable' alert, in force since November 2015, responds to 'credible' intelligence information, according to which a group of people has both the intention and the ability to carry out a terror attack in Australia.
