A spokesman for the agency confirmed that advanced negotiations were taking place and a deal was imminent. The agency was unable to give precise details of the nature or scope of the remit.
Industry sources suggest the account will focus on consumer work, but details of The Outside Organisation's remit are yet to be finalised.
Ticketmaster, which originated in the US, is owned by USA Networks, owners of travel website Expedia and the USA Entertainment Group, the film and TV maker that appointed ex-Channel 4 chief executive Michael Jackson as president and CEO last year.
The Outside Organisation, founded by former punk bands manager Alan Edwards, counts footballer David Beckham and his singer wife Victoria among its clients.