Priest, who is also executive chairman at market research agency SPA, has previously partnered with Tpoll to offer his clients online insight tools.
He takes up his position as non-executive director following the management buy-out of Tpoll from Interactive Prospect Targeting Group late last year.
In his role as non-executive director, he will provide independent advice on issues such as company strategy and performance.
He will also informally work with Tpoll's CEO Mark Ursell on a more flexible basis to offer guidance and support to the business.
According to Priest SPA saw the trend for online research as clients sought different mediums to reach an increasingly technology-savvy population, which brought the agency to work with the online specialist Tpoll.
Priest said: "Following the management changes in 2008, Tpoll is currently in a strong growth position as it boasts an impressive technology platform that has been developed in-house, alongside a team of market research professionals which enables it to deliver truly bespoke online research solutions.
"With a growing customer base of well-known brands and market research agencies, it is an exciting time for Tpoll," he said.
Ursell said: "Jon has 25 years' of experience within the market research sector. SPA is now one of the leading independent full service research agencies in Europe which clearly demonstrates Jon's talent for managing a successful and sustainable research business.
"His on-going input and advice will be invaluable as Tpoll begins this new phase of growth."