The agency retains the offline buying on the business while adding the online planning and buying, previously handled by Profero. It will also add strategic planning to its responsibilities, which was previously with Michaelides & Bednash.
M&B did not take part in the pitch process but is expected to maintain a reduced relationship with Channel 4 on projects.
OMD won the business after a final head-to-head pitch against ZenithOptimedia. Presentations were held last Thursday with Channel 4 making a swift decision and appointing OMD the next day.
The broadcaster had previously knocked the media agencies Aegis Media and Mediaedge:cia and the digital agency Profero out of the pitch process.
The pitch, which was called in May, was the first media review to be held by Channel 4 since it launched in 1982.