The agency scooped the business following a competitive pitch against three undisclosed shops.
John Pain, BP's head of marketing services and procurement, handled the pitch. It is understood that the company plans to appoint further digital agencies to the roster in the near future.
The review involved two briefs, the first of which will see Agency Republic produce digital advertising to promote BP fuel brand Ultimate Fuel.
The online campaign will position the premier fuel, which is engineered to give vehicles better performance while reducing the emission of harmful gases, as an eco-friendly alternative.
It is thought that the agency will then take responsibility for creating a one-off global campaign, the details of which have yet to be disclosed.
The creation of a digital roster is part of a wider push to promote BP's green credentials. It recently hired Chemistry Communications to handle its "Target Neutral" campaign, which urges drivers to offset their CO2 emissions.
A spokeswoman said: "We are exploring several ideas with a number of agencies."