The WPP-owned agency beat competition from OMD, Carat and ZenithOptimedia.
The UK section of the business was previously handled by ZenithOptimedia's digital specialist, Zed Media.
The online recruitment agency is investing heavily in online advertising.
The review, which kicked off in January, included a brief to develop a pan-European digital strategy.
The business includes the German and French markets, with the UK said to be worth £10 million.
Monster.com spent just £2 million on advertising in the the UK last year, according to Nielsen Media Research, but is planning a heavyweight campaign for later this year. The online recruitment market is booming and, according to the World Advertising Research Council, is now worth around £100 million.
Monster.com is also reviewing its European creative account. The UK portion of the business is currently held by Leo Burnett.
The move follows a wider pan-European repositioning for the brand, after it acquired a number of rival websites.
Leo Burnett won the UK account without a pitch in December 2005 from Saatchi & Saatchi.
The recruitment company is also seeking an agency to handle online communications to candidates and potential advertisers.
Monster Worldwide reported a 24 per cent increase in total revenue to $266.6 million (£153.2 million) in the fourth quarter of 2005.
Mediaedge:cia and Monster.com were unavailable for comment as Campaign went to press.