Faheem Khalid Lodhi, 36, was charged with planning to blow up the electrical grid in the city of Sydney as well as several defence sites in 2003.
The Sydney architect was convicted on three terrorism-related charges in June and faced a maximum sentence of life in jail.
The prosecution claimed that Lodhi, who denied four counts of preparing to commit a terrorist act, had "the intent of advancing a political, religious or ideological cause, namely violent jihad."
Prosecutors linked Lodhi, also known as Abu Hamza, to Frenchman Willie Brigitte, who was deported in late 2003 after being accused of plotting a major attack in Sydney.
Brigitte, who remains in custody in France, is suspected of links to al-Qaeda.
Both Brigitte and Lodhi are alleged to have trained with Lashkar-e-Taiba, a militant Pakistani group that Australia has banned as a terrorist organisation.
Lodhi was convicted of acting in preparation for a terrorist act by seeking information about chemicals capable of making explosives.
He was also found guilty of possessing a so-called "terrorism manual" and of buying two maps of the electricity grid, connected with preparation for a terrorist act.
Lodhi has denied that he had any intention of launching an attack.
"This country is my country and these people are my people," he said while giving evidence in his own defence. "The killing of innocent people is not part of Islam."
Supreme Court judge Anthony Whealy sentenced Lodhi to a maximum of 20 years jail with a non parole period of 15 years.
’Sentence appropriate’
Attorney-General Philip Ruddock said the stiff jail sentence handed to Lodhi fits the crime.
"The sentence reflects the seriousness of the offences," a spokesman for Mr Ruddock said, adding that it was not appropriate to say more because Lodhi still had time to lodge an appeal over his sentence.
Meanwhile the prime minister, John Howard, refused to comment on the sentence, saying it was inappropriate for him to comment on judicial matters.
He said his role was to help enact laws, not enforce them.
"I think it's important that I do not get into a situation of commenting every time there is a court decision," Mr Howard told reporters at Tumbi Umbi, on the NSW central coast.
"The Australian public knows how much I am opposed to terrorism."
Mr Howard repeated his pledge to maintain and strengthen Australia's anti-terrorism laws where necessary.