Previously, the company's direct business was handled by several different agencies and its in-house team.
AOL has briefed Joshua to create a mailing campaign aimed at potential new customers, before working on other forms of customer relationship management, taking in online and email work.
The agency's appointment comes as AOL significantly boosts its marketing budget to compete with broadband market leader BT.
AOL, which has more than 2m customers in the UK, last year spent more than £42m on advertising, according to Nielsen Media Research, but this figure is expected to be exceeded in 2004, as it has stepped up promotion of its broadband services, backed by an increased focus on TV.
Direct activity, which will take the theme 'Opening up a world of possibilities', will tie in with AOL's advertising, by Grey London.
In October AOL launched a campaign tapping into the popularity of music downloads. The work, which featured a Chinese Elvis impersonator, was intended to broaden awareness of the ISP's array of music content.
AOL is reviewing the structure of its marketing department following the resignation of vice-president of marketing Sharon Lang, who is quitting in the new year to return to consultancy (Marketing 1 December).