Focus groups, staff, volunteers and the general public will all be consulted to develop the brand, and Cascaid will create a guide on communications, visuals and literature based on the views expressed.
Charles Looker, NAS marketing manager, said: "Rather than change our name and logo we are looking at developing what is behind the logo. We've chosen to work with Cascaid because we believe they understand our needs and can make our brand work harder for us."
NAS chose Cascaid over three other agencies that pitched due to its personal ties with autism and its previous charity marketing experience. Two members of the Cascaid team have children with autism and the agency counts Alzheimer's Society, British Heart Foundation and Mencap among its clients.
Alan Clayton, managing director of Cascaid said: "We are a powerful specialist team that can confidently determine what is needed to drive all aspects of fundraising, marketing and communications for a cause so close to our hearts."