Abbott Mead Vickers BBDO, Arnold London and Scangroup in Africa are pitching for the account.
The successful agency will be briefed to create an integrated campaign designed to build on the brand's popularity in Kenya.
It will then be developed outside of Kenya in an attempt to grow sales across East Africa, in countries including Uganda, Tanzania and Ethiopia.
The winning agency will create a brand campaign, which will then be implemented by local agencies.
The pitch began earlier this year and is now in the research stage. A result is expected soon, with first work for the brand scheduled to appear in September.
It is the first time the company has considered agencies from outside of Africa.
Tusker lager is owned by East African Breweries as part of a joint venture with Diageo.