A guarantee of access to a local doctor 12 hours a day, seven days a week will be promised in the Conservative Party's election manifesto.
The policy will ensure that everyone will be able to see a GP in their local area, David Cameron will say.
The Tories have been critical of current opening hours and out-of-hours access to health services, with a quarter of GPs' practices closing by 6.30pm during the week, they say.
Mr Cameron is hoping the promise will win votes and prove the party can be trusted with managing the NHS, a policy area which has traditionally been seen as Labour territory.
The Tory leader sought to reinforce his centrist credentials in an interview with the Sunday Telegraph, in which he pledged to govern on behalf of "everyone in Britain" if elected.
He said he would avoid the more "divisive" policies associated with the Thatcher governments of the 1980s, instead urging the country to "join together, act decisively and move forward with optimism".
The manifesto document is also due to include commitments to give troops greater support and offer the public shares in nationalised banks - as well as previously publicised promises such as halting planned National Insurance rises and giving tax breaks for marriage.