Mallard also announced a new executive wing annexe will be constructed for ministers.
The old earthquake-prone press gallery building at the far end of the Parliamentary precinct will be demolished to make way for the extra ministerial offices
A two-storey building will also be constructed for parliamentary security.
The money for the new builds has not yet been revealed but Mallard said the funding has been sought so it would come out of next year's Budget.
In a statement, Mallard acknowledged that the plans would require "significant investment".
"However, we must look at the long term," he said.
"Ultimately, this is the right and responsible course of action to ensure our nation's Parliament is supported to operate efficiently and effectively for many years to come."
The goal is for all the new buildings to be completed and ready for use following the 2026 election.
Mallard had considered using the new "fast track" provisions –designed to boost construction work as part of the Covid-19 recovery - to consent it.
But after discussions with the Minister of Finance and Environment Minister David Parker, decided that was inappropriate.
NZ First has twice scuppered plans for new buildings on Parliament's grounds.
Mallard said if NZ First got back in in 2023 and demanded the project be dropped, he would put a picture of former NZ First MP Shane Jones on the side of the unfinished building.
In a statement, Mallard said it was his firm belief that this strategy needed to be revisited.
"We must take this opportunity to ensure that the precinct is well-positioned to support Parliament as it evolves over the next 50-100 years."
Mallard said this has been agreed to by all political parties.
"For many years now, it has been clear that current accommodation on the parliamentary precinct is not fit for purpose and can no longer effectively support a modern, accessible Parliament."
He said the move makes absolute sense financially and logistically.
Speaking to media on their way into caucus meetings this morning, a number of MPs were asked what they would like to see included in Mallard's designs.
National's Matt Doocey came up with the idea of a group hug room while Deputy Prime Minister Grant Robertson suggested Jacuzzis for the Press Gallery.
Museum St Building
This will be built on top of what is now car parks next to Parliament House.
Although Mallard is still applying for resource consent, he said it will have a modern design, which will be "sympathetic to the surrounding environment".
"We are not seeking to create a landmark."
The six-story building will have a direct link to Parliament House, will have a Green Star rating of six and will offer a "high degree of flexibility".
New ministerial offices
This will replace the old press gallery offices, which were vacated in 2017 due to earthquake strength issues.
The plan is for that building to be knocked down and to be replaced by the new structure. It will be a three-story building, complementary to the existing Executive wing, with a link to Parliament House.
It will also have a Green Star rating of 6.
Security building
This will be two stories and is proposed to be built at Ballantrae Place entrance. It will accommodate the current "secure deliveries" functions, the processing of inwards and outwards goods and security screening for contractors.
