The Deputy Prime Minister will hail the by-election victory in Eastleigh as proof that the Lib Dems can succeed as a party of government.
He will also dismiss the "myth" that being in coalition has undermined their identity or ability to fight the Conservatives.
The rallying cry comes in a keynote speech to the Lib Dem spring conference in Brighton.
The leadership has been eager to use the gathering to move on from damaging allegations of sexual harassment by Lord Rennard - which he denies - and the conviction of former Cabinet minister Chris Huhne.
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Ed Miliband will order an emergency recruitment drive of nurses so an extra 20,000 will be working in the NHS by 2020.
Sir John will give a speech later today saying a Labour-SNP government would be "weak and unstable" and wreck Britain's economic recovery.
Nigel Farage has told ITV News he would "happily" accept Christian refugees into Britain because they have "literally got nowhere to go".