Despite acknowledging his party is unlikely to be in power alone, the Deputy Prime Minister will pledge a series of "independent" LibDem policies.
Although his party has been in power for four years he will also say that "Britain doesn't want or need simply 'more of the same".
The LibDems are struggling to regain momentum after recent disastrous European and by-election results. But Mr Clegg will today strike a defiant tone, saying his party will fight the election on its own terms. The manifesto "will not be written with an eye to what Labour or the Conservatives think or might sign up to," he will say.
Instead, it will "be written as an answer to one, simple question: how can we build opportunity for all?"
In what will be seen as a dig at the Tories, he will reiterate his belief that it would be wrong to continue with "austerity as usual".
And he will warn that until Labour "come forward with a coherent plan to deal with Britain's fiscal problems, they're just whistling in the wind".