Mother scooped the creative work from competitors Partners BDDH, Publicis and WCRS.
Incumbent BMP DDB, which has handled ONdigital's £27m creative business since the service launched two years ago, was not asked to repitch.
Jeremy Dale, sales and marketing director for ONdigital, said in a statement, "Rebranding the business as ITV Digital presented us with the opportunity to consider a new creative direction and we put the creative work out to competitive tender".
The overhaul is part of a restructuring at commercial TV channel ITV, which will see more cooperation between ONdigital shareholders and ITV partners Granada and Carlton Communications.
As ITV Digital, the service will be able to take advantage of cross-promotion opportunities on its sister terrestrial TV channel, which had been unavailable to it as ONdigital because of broadcasting regulations.
Mother will also handle the launch of new premium pay-TV channel, ITV Sport, which ITV hopes will increase the brand's penetration in cable and satellite homes.
ONdigital currently has 1.1m subscribers. It hopes that take-up of the sports channel will give it the extra push it needs to break even in 2004.