A 30-year-old Victorian man has been accused of setting fire to old Parliament House last Thursday. He has not been named but will appear in court in the ACT on Tuesday.
He is the fourth person to be charged after last week's fire which destroyed part of the historic building.
The other three have not been charged with arson. Two have been accused of assaulting police officers and the third with "hindering a territory official".
Of the four now charged, at least three are from outside the ACT. One is from Byron Bay and a self-proclaimed anti-vaxxer.
Two people appeared in court on Sunday while the third was said to be unwell. One was charged with three counts of assaulting a "frontline service provider", the second was charged with one count of assaulting a "frontline service provider" and the third was charged with hindering a territory official.
The maximum prison sentences for damaging Commonwealth property and arson are 10 and 15 years respectively.
Police have formed a taskforce to go though video of the scenes at the doorway to the historical building and interview witnesses.
"The Taskforce under Operation Pike will continue investigations to identify other people involved in the fire and other criminal activity and further arrests may occur," the police said.
"Anyone with information that could assist police in relation to criminal activity in the Parkes, ACT, area over the past two weeks is urged to contact Crime Stoppers on 1800 333 000."
After the fire, police said the establishment of the taskforce "underscores the zero-tolerance authorities have for violence, destruction of property and assaulting police.
"Those who break the law will be arrested and charged."
The blaze burnt the front doors of Canberra's heritage-listed building, causing "tragic" and potentially irreparable damage according to Museum of Australian Democracy director Daryl Karp.
Thursday's fire broke out amid a protest at the entrance and also caused extensive damage to the portico.
Police confirmed officials had agreed a small smoking ceremony could take place as part of a peaceful protest but said it got "a little bit out of hand".
Aboriginal Tent Embassy activists distanced themselves from the protest, saying a smoking ceremony that took place did not have knowledge or consent from the Embassy Council.
The director of the Museum of Australian Democracy said after the fire that closing the building due to "violent protests" was "really tragic".
She said further examination was needed to determine if damaged parts of the heritage-listed building could be fixed, with the doors "pretty damaged" and the portico "really burnt out".
"The portico was built specifically for the Queen's visit in the '50s and so it has substantial significance, as do the doors which are from 1927," she said.
"It's unclear whether we can restore the doors or not. Obviously they are pretty significant collection items and that's a really big one for us."
Ms Karp said the lower gallery floors had original lino covering from 1927.