But Mr Truss is not expected to step aside as deputy PM until March 17.

It was also revealed yesterday the government’s Trade Minister, Andrew Robb, will also announce his departure today.

Fairfax Media was told Mr Truss, who has led his party since December 2007 and was first elected in 1990, had spoken at least twice to Prime Minister Malcolm Turnbull about his future.

It’s understood in conversations that took place in January and then again earlier this month, Mr Turnbull asked Mr Truss to delay his retirement.

The long-serving Nationals leader had been prepared to stand aside on both occasions.

The long-foreshadowed changeover follows a long period of speculation in which the resignation of the veteran leader has been an open secret, but the timing of his departure has been kept quiet.

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 sufficient support to deny Mr Joyce his long-held ambition of leading the Nationals.

However, inside sources say widely reported 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”.