"I have today declared the siege a terrorist incident for the purposes of the Terrorism Insurance Act," Country's Treasurer Joe Hockey said on the December 15 incident.
The declaration would prevent insurers from refusing affected businesses claims, even if their policies excluded losses from acts of terrorism.
The businesses affected by the incident had made claims totalling around USD 600,000.
"I am pleased to see these companies acting so responsibly at this difficult time," he said.
Iranian-born ISIS sympathiser Man Haron Monis had shot dead one of the hostages, cafe manager Tori Johnson, at close range during 17 hours long Lindt-cafe seige.
During the siege, 12 hostages including two Indians managed to escape before officers from the Tactical Operations Unit smashed their way into the cafe at 2am after a sniper reported a hostage had been shot.