The blaze was quickly put out but marks an escalation in indigenous protests in Canberra.
Indigenous campaigners have been holding demonstrations in the lead-up to the 50th anniversary of the establishment of the Aboriginal Tent Embassy on the former parliament's front lawns.
The tent embassy was a protest occupation site that launched national discussion about indigenous land rights. It has been a permanent fixture on the lawns outside Old Parliament House since 1992 but is not always occupied.Australia's parliament moved to a new building a short distance away on Capital Hill in 1988, but the Old Parliament House has remained as a museum and national heritage site.
Government leaders condemned the attack on Thursday, with several describing it as an "attack on democracy". "Setting fire to a building is not a lawful protest, it is a crime and a serious one," tweeted the deputy prime minister Barnaby Joyce. His predecessor, and current MP, Michael McCormack said: "Old Parliament House is on fire with protesters screaming "Let it burn! Let it burn!" How disgraceful. An outrageous attack on our democracy, our history, our sovereignty. This modern penchant for tearing down our past serves no purpose."You might also be interested in: