After more than a year of speculation, the ABC has confirmed Attorney-General George Brandis will leave Parliament to take up the post of Australia's High Commissioner to the United Kingdom.

Key points: George Brandis entered federal parliament in 2000, became A-G in 2013 when Tony Abbott won the election

George Brandis entered federal parliament in 2000, became A-G in 2013 when Tony Abbott won the election Main contenders to replace him are Christian Porter and Michaelia Cash

Main contenders to replace him are Christian Porter and Michaelia Cash Senator Brandis replaces Alexander Downer as High Commissioner

Senator Brandis' move to London opens the way for a ministerial reshuffle — it is likely to be announced tomorrow.

The senior Cabinet role of attorney-general is tipped to be filled by either Social Services Minister Christian Porter or Employment Minister Michaelia Cash.

Both are already in Cabinet and both are from Western Australia.

Mr Porter appears the frontrunner, having previously served as WA attorney-general and as a public prosecutor.

The position of special minister of state is also vacant because Liberal senator Scott Ryan became Senate President last month.

Finance Minister Mathias Cormann has been acting in the role.

The vacancy is for the portfolios that were held by former Nationals deputy leader Fiona Nash, who lost her Senate position and her role in the ministry when she was found to be a dual citizen.

Nationals senator Bridget McKenzie has replaced Senator Nash as deputy leader and is likely to take on former senator Nash's positions as minister for local government, regional communications and regional development.

Senator Nash is set to be replaced by a Liberal in the Senate which would mean the Nationals could technically lose one Cabinet position.

But it is expected Prime Minister Malcolm Turnbull will let the Nationals keep five Cabinet positions, which will anger some Liberals.

The other big change in the ministry is the already announced decision to make Peter Dutton the Home Affairs Minister.

Mr Dutton's new super-ministry will incorporate ASIO and the Australian Federal Police, as well as immigration.

The other recent disruption to Cabinet has been that Liberal senator Arthur Sinodinos has been on leave from his role as Industry and Science Minister since September because of a health problem.

Brandis ends on high note with impassioned Senate speeches

Senator Brandis will replace Alexander Downer, the long-serving foreign minister in the Howard government, as Australia's High Commissioner to the UK.

Mr Downer has been in London since 2014.

Senator Brandis entered federal parliament in 2000 and has been Attorney-General since Tony Abbott won the 2013 election.

He was shadow attorney-general from December 2007.

Senator Brandis has often been regarded as one of Parliament's more reserved characters.

But in recent months, the Attorney-General has garnered praise for his more impassioned stance on a number of issues.

Among them, slamming Pauline Hanson for her "appalling" decision to don a burka during Senate Question Time, and his eloquent speeches during the same-sex marriage debate in advocating for a change to the law.

He was visibly emotional after Parliament passed the legislation earlier this month.

Sorry, this video has expired Brandis gives the last speech on the SSM bill before amendments (Photo - ABC News: Jed Cooper)

Despite those recent examples, Senator Brandis will also be remembered for some spectacular own goals.

His bitter public feud with then solicitor-general Justin Gleeson played out in front of television cameras, with the nation's chief counsel arguing he lay awake at night concerned Senator Brandis was further trying to curtail the independence of his office.

Mr Gleeson resigned over what he described as a "broken" relationship with the Attorney-General, before joining the case against Deputy Prime Minister Barnaby Joyce in the citizenship fiasco.

As the nation was debating the need for the Government to have greater access to the public's digital information, the Attorney-General struggled to explain what metadata was during a live television interview.

He also spoke in Parliament of the "right to be bigots" during discussion over racial discrimination laws.