John Gilbert Gordon of Caboolture in Brisbane pleaded guilty and was jailed for two-and-a-half years by a local district court today.
The prosecution told the court that the old man began his "campaign of terror" in 2007 by sending a flurry of letters to leaders including Gillard, her predecessor Kevin Rudd and leader of the Opposition Tony Abbot.
The mailed threat letters contained explosive packages, including bullets and detonators, and spoke of carrying out fire bombings.
Gordon, whose antics were sought to be blamed by his lawyer on his "cranky mood", was found after forensic experts traced a threat letter to Tony Abbot to his notepad, which carried impressions of his name.
In the letter, Gordon had threatened to poison water supply at a motel housing asylum seekers, saying "We will wipe out all foreigners on Australian soil".
The judge took a lenient view of his actions because of his age but observed that "His actions were very serious".
