The agency was brought in after a competitive pitch involving incumbent Bell Pottinger Public Affairs, Weber Shandwick and Brunswick.
The MSA is looking to bring in an amendment to the Road Traffic Act, which currently does not allow road laws around speed limits and road-worthiness of cars to be temporarily changed for motor events.
This means that motor sport events cannot take place on UK roads, apart from a small number of races that have been provided with specific amendments, such as the Isle of Mull Rally and the Jim Clark Rally in Scotland.
The ability to temporarily suspend road laws sought by the MSA is already in place across Europe. The Portland team, led by head of Portland Local Kevin McKeever, will combine grassroots campaigning with the MSA's local clubs to target Westminster and the media. The aim is to deliver a change in the law by the end of this Parliament.
McKeever said: 'The MSA's campaign plays to Portland strengths: strong understanding of local government, combined with an industry-leading track record at Westminster and with the media.'
Ben Taylor, director of development and comms at the MSA, said: 'Portland impressed us with its excellent understanding of our challenge and detailed, creative response to our brief.'