The territory has reached an agreement with the federal government to remove firearms under the scheme, which was set up following the Bondi mass shooting in December.
It is just the second jurisdiction to do so after NSW announced last Sunday it would be part of the buyback.
It's estimated 14 per cent of the ACT's 7000 firearms licence holders will be affected by a proposed cap on guns.
There are 23,000 guns registered in the national capital.
Home Affairs Minister Tony Burke says 75 per cent of the cost of compensation to firearm holders, administration and gun destruction will be paid for by the federal government.
"We know most firearms, the overwhelming majority of firearms, are held by good citizens who will never use them for an improper purpose," he told reporters in Canberra on Saturday.
"But there were concerns from the Australian people as to how individuals such as those at Bondi ... had the number of firearms they'd been licensed with had been approved to get firearms at all."
Mr Burke said two firearm types - straight pull and assisted repeating - had been reclassified to take them away from recreational shooters, and provision had been made for this to work across the board.
"We've designed the buyback to make sure it can match the different way that different jurisdictions are dealing with this," he said.
Prime Minister Anthony Albanese said on Friday the government would work closely with the ACT to keep more guns off the streets.
"National gun reform is an important part of making sure an anti-Semitic terrorist attack like we saw at Bondi can't happen again," he said in a statement.
While agreeing the majority of gun owners were responsible, ACT Chief Minister Andrew Barr said further safety measures were needed.
"The buyback scheme will provide compensation while helping deliver further community safety outcomes," he said.
"The ACT has some of the strongest firearms laws in the country and this agreement supports our ongoing efforts to further reduce the risk of firearms falling into the wrong hands."
National cabinet agreed to strengthen firearm restrictions across Australia following the Bondi attack, where 15 people died after two gunmen opened fire at a Hanukkah festival.
But the scheme faces opposition from some jurisdictions, with conservative governments in the Northern Territory, Tasmania and Queensland declining to sign up.
Western Australia had already operated its own gun buyback and does not have plans to be part of a second one linked to the federal government.
However Mr Burke said what mattered right now was that a second jurisdiction had decided to be part of the federal scheme.
"A second jurisdiction deciding what we were all saying straight after the horrors of Bondi that we needed to be able to deal both with the motivation and the method."
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