Opposition Leader Bill Shorten has defined the first Coalition budget as a test of leadership, economic management and, ultimately, honesty, saying the government was already deceiving voters over the state of the budget.

He will use a speech in Canberra on Wednesday, his first address as Opposition Leader to the National Press Club, to explain his approach and call on the government to be more economic and less political with its decisions.

Consensus man: Bill Shorten. Credit:Alex Ellinghausen

Laying out a new, ''inclusive'' agenda for Labor, Mr Shorten will argue his party must change in order to reach beyond its traditional union and inner-city electoral base while also protecting its legacy.

The speech comes less than two months before the budget and coincides with an analysis of official figures from the independent Parliamentary Budget Office showing Labor left the budget in better shape than the government admits.