The site, heatworld.com, will feature breaking celebrity news, video clips and fashion and beauty product reviews alongside blogs by Heat journalists.
It will also create a celebrity-focused social network, enabling users to post profiles, comment on stories and join forums.
The launch of the site, revealed in Media Week last year, comes eight years after Heat's news-stand debut.
After a difficult start as a men's entertainment magazine, it was revamped as a celebrity weekly and now sells 598,623 a week.
Louise Matthews, managing director of Emap Entertainment, who led the relaunch seven years ago, recently announced she would step down to take up a part-time consultancy role with the media group.
Julian Linley, launch editor of First who moved onto the online project last year, will oversee ongoing development as the brand's digital editor.
Emap's digital head of sales, Kurt Edwards, will handle the commercial opportunities.
The announcement followed yesterday's resignation of Emap chief executive Tom Moloney, which has renewed speculation of a break-up of the company.
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