The roster, which also includes agencies across design, media planning, broadcast, web development and market research, is worth up to £2m.
Grayling, Seashell Communications and JBP are the new PR entrants to the line-up, replacing Golley Slater and Admiral PR, while Coast Communications and Kor Communications successfully repitched.
Devon County Council marketing and comms manager Sam Hill said: "Key areas for us will include public health due to our ageing population, so that’s likely to cover issues such as dementia and winter flu jabs.
"There’s also a need to encourage growth, and promote the job opportunities we have here in areas like tourism, construction and technology. We want to drive forward these opportunities so we don’t have an outward migration of our skilled workforce to look for jobs elsewhere."
All local authorities in Devon will be able to use the roster for the first time, in a move reflecting wider efforts to unify public sector comms regionally.
Hill added: "It’s about working more efficiently, and being more co-ordinated in our approach. The move of responsibility for public health to councils this summer shows how the lines are blurring between authorities so there’s a need to share forces and budgets."