The pay-TV company is expected to formally kick off the review process in March via a request for information from its procurement department.
Sky, which this week posted an 18 per cent rise in profits, has already alerted its roster agencies about the forthcoming review and its intention to appoint a lead direct marketing shop.
The bulk of Sky’s direct marketing is handled by Digital and Direct, which has worked on the business for the past 13 years. In September last year, the agency was acquired by SapientNitro in a deal worth £26 million.
However, Sky has also worked with a number of other direct marketing agencies on a project basis.
Recent activity created by Digital and Direct for Sky includes "Sky at the O2" and an "introduce a friend" campaign to increase subscribers.
This resulted in the appointments of agencies including 20:20, Elvis, Brothers and Sisters, Efficient Frontier and its advertising agency WCRS.
A Sky spokesman said: "We’re about to review our below-the-line agency support and will invite a number of agencies, including our incumbents, to enter into the that process."