Mr Robb entered politics in 2004 when he won the safe Victorian seat of Goldstein. He had previously served as Liberal Party federal director from 1990 to 1997, a stint which included the triumphant 1996 election win for John Howard, and a stint as the executive director of the National Farmers Federation. Nationals Leader Warren Truss may bring forward an announcement on his future to Thursday. Credit:Andrew Meares In a statement, Mr Robb said that at age 64, "I plan to move on to my next career, which will be in some capacity in the private sector. I will leave politics in the comfort of knowing that both the Turnbull government and the Coalition are in great shape. It's an opportune time to hand over the baton to the talented next generation in our party." "I have been given some wonderful opportunities to serve our country by both Tony Abbott and Malcolm Turnbull, and for that I will be eternally grateful." Human Rights commissioner Tim Wilson and Chamber of Commerce and Industry economics director John Osborn are two of the names already being discussed by Liberals to replace Mr Robb in Goldstein.

Mr Truss's announcement will ratchet up positioning within his party to replace him as leader. A source close to Andrew Robb confirmed the Trade Minister will resign. Credit:Fiona Goodall It also brings into sharper focus the need to replace junior minister Jamie Briggs, who resigned from the Cities portfolio over Christmas, as well as the likely replacement of Mal Brough, who is currently stood down pending a police investigation relating to his connection to the Ashby-Slipper affair. A third vacancy could also arise if advice from the Secretary of the Department of Prime Minister and Cabinet, Martin Parkinson, finds Human Services Minister Stuart Robert breached the ministerial code of conduct when travelling "privately" in China in 2014. Two wrongs don't make a right, Deputy Prime Minister Barnaby Joyce says. Credit:Alex Ellinghausen

A ballot for the Nationals leadership is not, however, certain to take place as deputy leader Mr Joyce is strongly favoured to take the leadership post and the deputy prime ministership. Fairfax Media has been told that Mr Truss, who has led his party since December 2007 and was first elected in 1990, has spoken at least twice to Mr Turnbull about his future. Insiders say suggestions Riverina MP Michael McCormack was a contender for the role of leader were a combination of wishful thinking and mischief-making. Credit:Andrew Meares It's understood that in conversations that took place in January and then again in February, Mr Turnbull asked Mr Truss to delay his retirement. Mr Truss had been prepared to stand aside in January, before Parliament returned, and then again in early February.

Mr Turnbull has, in addition, at no stage pressured the Nationals leader so he could bring forward his frontbench reshuffle. The long-foreshadowed changeover follows a protracted peri-retirement phase in which the resignation of the veteran leader had been an open secret, but the timing of his departure had been kept quiet infuriating leadership hopefuls. Tensions between Mr Truss and Mr Joyce, the heir-apparent, have been cited as the reason for the delay, with claims Mr Truss had been deliberately holding out, hoping the extra time would allow an alternative candidate to gain support sufficient to deny Mr Joyce his long-held ambition of leading the Nationals - a post which comes with the deputy prime ministership thrown in when in office. Party sources said suggestions that Riverina MP Michael McCormack was drawing level with Mr Joyce in the undeclared race for the leadership was a combination of wishful thinking and deliberate mischief-making, while another said it was merely an attempt to build on momentum "that isn't there". Joyce forces say at the very most, Mr McCormack can assemble 7 votes in the 21-member party room. "It's not even close," said one Joyce backer.

While Mr Joyce enjoys the strong backing of the party room, the race for the position of deputy is harder to pick. That post comes with the allure of a cabinet membership. Mr McCormack's chances would appear to be enhanced if he elects not to run against Mr Joyce for the top job, because as one MP noted, the Joyce forces will hardly thank him for trying to knock off the favourite. Among the likely contenders for second-in-charge are the current deputy leader of the House and Minister for Vocational Education and Skills, Luke Hartsuyker, and Queensland backbencher Keith Pitt. The talented Victorian Darren Chester, is also expected to throw his hat into the deputy leadership ring. Once a new leader is chosen, Mr Turnbull can turn his mind to what portfolios the Nationals will hold, and whether the junior party's representation in cabinet should rise from three to four -considered a strong prospect. Late last year, Mr Truss, seen as much closer to Tony Abbott than to his urbane replacement, attempted to engineer the secret defection from the Liberals to the Nationals of the dumped former resources minister, Ian Macfarlane. The move failed but not before exposing Mr Truss's involvement in a plot that undermined Mr Turnbull's authority - hardly an ideal situation between Prime Minister and Deputy Prime Minister.

Opposition leader Bill Shorten said the resignations meant cabinet was in "chaos" and that "it's only a matter of time before Malcolm Turnbull stands in his courtyard to tell Australians that 'good government starts today'." Follow us on Twitter