The agency has been asked to create an integrated campaign for the new ITV2 drama series Belle de Jour.
Mother, which picked up the project without a pitch, will work with ITV's in-house agency, ITV Creative, and its newly appointed digital agency, Dare, to develop an integrated campaign for the series, which airs in autumn.
However, ITV said the appointment did not affect its relationship with M&C, which will continue to work on ITV1 and ITV Consumer, including the launch of itv.com.
The appointment follows the promotion of David Pemsel, the group marketing director of ITV, who replaced Clare Salmon in January. Salmon appointed M&C to handle ITV's account in 2005.
Stef Calcraft, a partner at Mother, said: "We are delighted to be involved in an assignment which has such potential to break new ground."
Mother has strong credentials in building and marketing TV brands. It launched five in 1997 and was behind ITV Digital's "monkey" campaign.