Cadbury will report to Matt Hunt, Adconion Media Group's UK managing director and will lead the Joost team as it develops from a video network to a broadcast platform for content and video.
Cadbury joined Adconion Media Group as director of media in June 2010. Prior to joining Adconion she was senior director of sales and Strategic Partnerships at Vibrant Media. She has also held positions at Agency Republic and Mindshare.
Hunt said: "Maria has an excellent reputation in the industry from her commercial experience with agencies and with publishers. She has a deep understanding of how brands are looking to engage with audiences, irrespective of the device or channel they are consuming."
Cadbury said: "Our objective is to make Joost the brand platform of choice for UK agencies deciding how to distribute video and content online.
"Joost addresses the market demand for a large-scale, dedicated, multi-channelled broadcast platform that delivers in-stream and in-banner video capabilities, across a number of devices."