The agency will be retained initially until the end of the year and will run the trade and consumer press office for the company.
Mischief has been asked to run a brand building campaign to create increased brand awareness among a wide range of potential customers including leisure and business travellers, young people and families.
The company is to launch an advertising campaign at the end of April.
MD Mitchell Kaye will head up the account, reporting to marketing manager Andrew Pumphrey.
Mischief replaces Lewis PR who has handled the account since January 2007.
LateRooms.com was bought by tour operator First Choice in 2006 for £120m.