Mitchell worked at the consultancy for the past five years, after previously working at Parys Communications and spending a decade Brunswick from the early 90s.
Friends and colleagues described Mitchell as "one of the most experienced crisis and corporate comms advisers they have ever worked with".
He had extensive experience advising companies through critical high-profile situations on a national and international scale, including media handling at the scene of the Paddington/Ladbroke Grove rail disaster, the riot at Yarls Wood immigration detention centre, and the public inquiry that resulted in the successful planning application for Terminal 5 at Heathrow.
During his time at MWWPR and previously at Parys, Mitchell was an adviser to the executive team at Four Seasons Healthcare, and was a key part of the comms team that worked through the current restructuring and sale process.
MWWPR UK managing director Rebecca Blinston-Jones described Mitchell as "professional and wise".
"Bob was always available and willing to help his colleagues, no matter how busy he was. He will be sorely missed by clients and colleagues alike," she said.
Outside of work, Mitchell was an active member of his local community and his family have asked for donations to be made in his memory to The Lyn Defibrillator Fund,instead of flowers.
The funeral will be held today at 3pm at the North Devon Crematorium in Barnstaple.