Glue won the account without a pitch and has begun working on a digital campaign incorporating online creative running on ANM's network and on non-ANM sites.
The agency will work with Wieden & Kennedy, which was appointed to promote the sites offline in March.
Dailymail.co.uk and mailonsunday.co.uk launched earlier this month.
Althought they appeared later than rival titles' sites such as Guardian Unlimited and Electronic Telegraph, they aim to attract 600,000 UK users a month within six months.
Rob Cooke, the ANM marketing director, said: "These brands are important to us and we want to ensure our digital advertising drives strong results. Glue impressed us with its track record of taking a highly creative approach to digital channels."
Glue will also work on the digital editions of two other Associated titles: the national property website, homesandproperty.co.uk, and ThisisTravel.co.uk.
W&K handles offline creative for the sites.
James Sanderson, the Glue marketing director, said: "We are excited to be working with ANM. It's another significant opportunity to demonstrate how creativity can really deliver in a digital campaign."