The pledge came as Sir Leon conceded that the commission had failed to provide companies with the 'quick decision-making and legal certainty they require'.
From next year the commission will let companies know whether or not a joint venture is to be approved within 'a few months' of being notified.
At present it can take years for the commission to decide whether it should approve or block joint ventures.
Under the new procedure the EC's competititon directorate will publish binding deadlines.
In the case of large-scale takeovers falling under the scope of the EC's merger regulations, the approval procedure takes a minimum of one month and a maximum of five.
Sir Leon said that, although it was not possible to replicate this procedure when examing joint ventures because of the commission's limited resources and the cumbersome legal framework within which it had to operate, he accepted the need for change.
Speaking at the Centre for European Policy Studies, he said: 'The commission must examine agreements and practices within a short period and provide legal certainty in a manner placing the least possible burden on industry.'
This was because it was often the case that deals could not be realistically unscrambled once implemented.
Sir Leon also said that Brussels was considering simplifying its mergers procedure by allowing notification forms to be filed with either the commission or competition authorities in member states.