The appointment, following a pitch process, comes ahead of a major awareness push by the company. Bwin, previously known as Betandwin, aims to promote its brand in the UK after recently launching its poker, casino and sports betting site in this country.
Bwin, which has 20 million registered users in markets including Germany, Spain and Italy, is expected to spend around £4 million on radio, print and online advertising.
Activity will roll out later in the first quarter as Bwin, which is based in Austria and launched in 1999, attempts to secure a presence in the highly competitive online gaming market.
Nic Wenn, Bwin's head of Northern Europe, said: "UM London showed a genuine passion for the challenge and an in-depth understanding of our consumer target."