Interstate visitors to Floriade are also expected to be attracted to the small ceremony at 2pm. The event will round off a series of firsts for this election in the ACT - the former Senate chamber at Old Parliament House was used for the first time to conduct the draw for the ACT Senate ballot paper, and the building was used for the first time as a polling place.

This use of the historic building on polling day was also popular, with people queueing for over an hour to cast their vote in King's Hall. They did not appear deterred by the long wait for their place in history.

On the day, Ian Gordon from the Australian Electoral Commission, went along the queue telling people about other places in Canberra where they could vote. ''Everyone decided they wanted to stay there; I can only presume they'd come to cast their vote in such a historic place,'' he told Fairfax Media on Monday.

Mr Gordon, the Australian electoral officer for the ACT, said King's Hall was selected for the formal declaration of the ACT Senate outcome because of its history.

"It is a historic and iconic site and, in terms of democracy, it seems like the appropriate place to conduct this sort of event,'' he said. On Tuesday Labor's Kate Lundy and Liberal Zed Seselja will be declared the winners of the two Senate places.

They will be sworn in to the Senate when Parliament resumes in several weeks for the first sitting of the Abbott government.

In the ACT Senate race, Labor's primary vote fell by 6.4 per cent, the Liberal Party failed to make a quota in its own right and 30,000 voters opted to vote for minor parties.

The ACT has the highest proportion of people voting below-the-line to choose where their preferences go. Each ballot paper had to be entered into the commission's computer system.

Mr Gordon has overseen the counting of votes for the ACT's two Senate places and two House of Representatives seats.

"We had just over 49,000 ballot papers below the line, which is about 20 per cent of the total ballots,'' he said.

"We had planned for 14 days of data entry leading to a declaration on the first of October and that's what we achieved.

"We were a little unsure how long it would take with 27 candidates this time compared to nine in 2010 and we were happy we were able to achieve it in that time frame.''

Old Parliament House now houses the Museum of Australian Democracy, which says King's Hall was the hub of the building.

''Open to the public from the earliest days, this space was far more than just a formal function room or foyer - it came to symbolise the openness of parliamentary democracy and representative government in Australia,'' its website says.

''Even in the 1970s, when new concerns about security led to the introduction of a separate entrance for the public under the front stairs, King's Hall remained open to the public.

''The openness of this old building now seems remarkable, particularly in comparison with the Australian Parliament House.

''King's Hall was the place where great public ceremonies were held, politicians and journalists mingled and prime ministers brushed shoulders with ordinary citizens.''