Mr Cameron says only his party is committed to 'openness'
David Cameron says the Conservatives would publish details of all government contracts worth more than £25,000, if they win the general election.
The Tory leader said his party would end what it calls "Labour's secretive and wasteful contracts regime".
Exceptions include Ministry of Defence and intelligence contracts, or those that might risk national security.
Mr Cameron made the pledge in a video-link address to the TED technology conference in California.
His party had already committed itself to publishing details of all public spending over £25,000 online and on Monday he claimed only the Conservatives were "at ease with openness" needed to reform politics.
But on Wednesday the party said it would begin publishing contracts with central government, quangos and government agencies online from 1 January 2011, if it wins the general election widely expected to be called in May.
It says "every commercially significant clause" will be put online - and all supporting documentation will be made available to the public.
The party says it will help people "root out wasteful spending" and help more small businesses win government contracts.
Initially, the Ministry of Defence and security services contracts would be excluded but the party says it intends to "develop a protocol for the inclusion of non-sensitive procurement by these agencies".
The Conservatives criticised the "worst" contracts entered into by the Labour government - including the £12bn NHS IT project and the abandoned £690m offender management system database, originally expected to cost £234m.
Ahead of his speech, shadow chancellor George Osborne said the government had wasted billions of pounds on "poorly negotiated and ineffective contracts".
"Our commitment to publish government contracts in full is the most radical transparency announcement ever made by a British political party - and will enable the public to hold ministers and civil servants to account like never before," he said.
"This policy will help us to cut government spending, root out waste and empower the public - and bring in a new age of transparency and accountability."