UP Communications will start work on the account immediately, in a campaign to drive awareness of the brand among consumers and within the fashion, media and tech industries.
It is the first time Style on Screen has hired a PR company.
Kingsley Maunder, chief executive and founder of Style on Screen, said: "We chose UP because it delivered a simple, smart and credible plan that will help us drive that success over the coming year."
Stuart Jackson, chief executive and founder of UP, said: "We just had a conversation about how we could move the business forward. Style on Screen is one of the most interesting and exciting companies I've seen working out of the Tech City area this year. Kingsley and the team have created a simple service powered by both complex technology and a true understanding of the fashion industry and the needs of its consumers."
Style on Screen is a web and Twitter-based fashion finder service which helps people find out what a celebrity is wearing on TV and buy it online.