By Jacob Shteyman in Canberra

The coalition will reunite after an acrimonious three-week split as Liberal and National leaders admit to putting supporters through a tough period.

Liberal leader Sussan Ley and her Nationals counterpart David Littleproud agreed on a deal to restore senior Nationals to the front bench after they were sacked or stood down for breaking solidarity conventions over hate-speech laws.

The pact was announced on Sunday in a joint statement promising a coalition that would look “to the future, not the past”.

“We acknowledge this has been a difficult period for millions of coalition supporters, and many other Australians, who rely on our parties to scrutinise the government and provide national leadership,” the two leaders said.

The agreement will see all former Nationals frontbenchers reinstated to shadow cabinet after a short sin-bin period.

Mr Littleproud offered for all former Nationals shadow ministers to spend two weeks on the back bench, while an offer previously put forward by Ms Ley would have seen them spend six months in parliamentary exile.

A compromise of six weeks on the back bench, backdated to the mass resignation on January 21, provided an end to the stalemate.

Mr Littleproud and deputy Nationals leader Kevin Hogan will immediately rejoin leadership meetings and shadow cabinet processes.

Frontbenchers will also sign formal agreements to codify the convention of shadow cabinet solidarity, in which MPs and senators must step down from their roles if they vote against an agreed position of the Liberal-National joint party room.

The position clearly sets out that the joint party room has primacy over the individual National and Liberal party rooms, addressing the contradiction that instigated the split.

Three Nationals frontbenchers – Ross Cadell, Bridget McKenzie and Susan McDonald – voted against Labor’s hate-speech laws, in line with a party decision but in defiance of an agreed shadow cabinet position to vote in favour.

The trio later tendered their resignations to Ms Ley, which she accepted.

But the move triggered a furious response from Mr Littleproud and the Nationals, who resigned from shadow cabinet en masse and caused the coalition collapse.

The reunification comes during a seismic shift in Australia’s right-wing political landscape, with minor-party One Nation surging past the former coalition partners in some polls.

Tensions between the Liberals and Nationals remain elevated after Mr Littleproud’s insistence the two parties could not get back together with Ms Ley at the helm of the senior coalition partner, seen by many Liberals as an unwelcome intervention in internal party affairs.