Initiative's appointment, which will include working across several European countries as well as the UK, comes as Vertu launches a range of luxury mobile phones.
Vertu, which began the search for a media agency last year, has also appointed Mediaedge:CIA to work in key Asian markets. It is not known what Vertu's creative arrangements will be, but it may not appoint a creative network, relying instead on work from smaller agencies.
Nokia announced the launch of Vertu in January with a separate management team. Its first product is a mobile phone cased in platinum with a crystal screen and high quality sound.
Initiative is thought to have been selected by Vertu because of its experience with prestige brands including LVMH and Patek Philippe.
Nokia's creative agency is Grey and its media agency is MediaCom. Neither is affected by Initiative's appointment. Vertu is creating a brand that is distinct from the main Nokia operation and so was keen to hold an independent process to select an agency. It is unclear which agency will develop creative for the brand.
Nokia, the world's largest mobile producer, hopes that the Vertu brand will create growth in the sector at a time when mobile sales are slowing.
Initiative Media refused to comment.