Prime Minister Tony Abbott is expected to reshuffle his ministry at the end of the year, ahead of a federal election due by September 2016.

Liberal sources say one of the highest profile changes could be Trade Minister Andrew Robb exiting cabinet and replacing former Labor leader Kim Beazley as ambassador to the United States.

Mr Beazley retires from the post in December, having already had his term extended.

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Mr Robb is familiar with Washington and has been widely applauded for his work in concluding trade deals with China, Korea and Japan and progressing talks with India.

Industry Minister Ian Macfarlane and Defence Minister Kevin Andrews are tipped to leave cabinet, with Mr Andrews also potentially being offered a diplomatic role.

While there has been talk of Mr Andrews replacing Bronwyn Bishop in the Speaker’s role, it’s expected within senior NSW Liberal ranks she will recontest her seat of Mackellar.

Nationals leader Warren Truss has been rumoured to be retiring from parliament after 25 years, but is understood to be firming in a decision to recontest his seat of Wide Bay.

Former WA state treasurer Christian Porter – who holds the seat of Pearce – is considered to be a likely winner from any reshuffle gaining a ministerial post.

Also mentioned as ministerial prospects are Hume MP Angus Taylor, Wannon MP Dan Tehan and government whip Andrew Nikolic.

– AAP