The digital media agency will initially work on new search marketing for BBC Magazines after a pitch against undisclosed agencies.
I-Level will work to promote the BBC Gardeners' World website at gardenersworld.com. It could also be handed work for other BBC Worldwide brands.
The win is I-Level's first reported account win since it lost two of its biggest briefs - Sky and the AA. The new business will also boost the independent digital agency, as speculation continues to mount about a possible takeover of the company. Aegis and AKQA are believed to have held talks with the agency, along with several other firms, but a final deal has not yet been reached.
PHD is the media agency for BBC Worldwide, and is the roster agency for BBC Worldwide's search requirements.
The Omnicom agency first picked up BBC Worldwide's media account in December 1998 and is not affected by the I-Level hire.
In the past week, Ed Ling, strategy development director, left I-Level to join start-up agency AnalogFolk, after nine years at I-Level.
Glen Conybeare, client services director at Generator, the consultancy arm of I-Level's parent company ILG, is also set to leave.
Both I-Level and BBC Worldwide confirmed that they are working together, but refused to go into details.
BBC Worldwide has signalled its intent to increase its online presence, having purchased a 75% stake in travel guide company Lonely Planet last October.
The commercial arm of the BBC said the brand's online potential was a major reason behind the investment, and developments are expected shortly.
Meanwhile, speculation persists that BBC Worldwide could be sold off by the public broadcaster, in a bid to raise more than £500m.
Today (Tuesday) marks the launch of another of BBC Worldwide's new projects: Match of the Day magazine. BBC Worldwide has resurrected the publication as a weekly title to compete against Bauer's Match and IPC's Shoot, which is being relaunched as a weekly title.
This article was first published on Media Week