Nick Clegg will be Britain's Deputy Prime Minister, it has been confirmed.
Downing Street said Mr Clegg's appointment had been approved by the Queen.
Mr Clegg will be one of five Lib Dem ministers in the new Cabinet, Conservative sources confirmed.
George Osborne has been confirmed as Chancellor of the Exchequer and William Hague as Foreign Secretary in the new Conservative/Liberal Democrat coalition Government.
Senior Conservative sources confirmed the two men retain the roles they held in the Tory shadow cabinet, scotching widespread speculation that the Chancellor's job might go to Kenneth Clarke or even Lib Dem Vince Cable.
Downing Street said no ministerial posts would be officially confirmed on Tuesday night, but reports suggested the deal struck between David Cameron and Nick Clegg's parties includes a promise of six seats around the Cabinet table for Liberal Democrats.
And it is expected that Mr Cable will be appointed Mr Osborne's number two as Chief Secretary to the Treasury.
Reports suggest Liberal Democrat David Laws will be made Schools Secretary and Tory Andrew Lansley Health Secretary - both also keeping their briefs from opposition. Tory Liam Fox was also reportedly given the post of Defence Secretary, again retaining his role held in the shadow cabinet.
The need to give jobs to Liberal Democrats means some members of Mr Cameron's shadow cabinet are likely to be awarded less senior jobs than they had been expecting in the run-up to the General Election, providing the first big test of his man-management abilities as PM.