The Museum of Australian Democracy, housed in Old Parliament House, had been closed for four months after it was set on fire by protesters and underwent intensive restoration after soot and ash spread throughout the building.

Its restoration, which cost nearly $5 million, included repainting the walls and wiping clean thousands of objects inside the museum.

It was both Mr Abbott and Mr Rudd's first event as patrons of the museum. Other prime ministerial patrons include John Howard, Julia Gillard and Malcolm Turnbull.

The museum's director Daryl Karp said a museum without people was a very sad place, without a heart and soul, especially during an election campaign.

The museum will open with a new exhibition five years in the making, titled Democracy DNA: The People, The Prime Ministers and The World.

"In my time here at the Museum of Australian Democracy, the most common comment we had from our visitors is they feel unheard. So we've sought to highlight and celebrate the many voices in our democracy," Ms Karp said.

Next week will also mark the 95th anniversary of Old Parliament House.

Mr Rudd spoke about the significance of democracy, even joking about losing the election to Tony Abbott in 2013 and noting the current situation in Ukraine.

"When we think of this term, democracy, it's no small thing and it can be snatched away. Look at what is unfolding in Ukraine today. There you have an authoritarian state, seeking to steal, not just the right for a country to exist, but also the system of democratic politics within that country," Mr Rudd said.

Mr Abbott spoke about the importance of the Museum of Australian Democracy, which is the only museum of its kind.

"This museum, this display gives people a very good taste of what it's like. So if you don't want to read the histories, if you don't want to delve into House of Representatives practice, come here, spend a couple of hours browsing, listen to the stories," he said.

Mr Abbott and Mr Rudd were later questioned by school students from St Mary Mackillop College, Wanniassa, and Bonython Primary School, who posed questions such as "what makes you a great leader?", "what motivated you to become prime minister?" and "what country is your family from?".

While the museum is now open to the public, restoration work is still ongoing, with the main entrance and parts of the building still covered in scaffolding. It is expected to be fully open by September.