Quince (above) held the same role at Porter Novelli, where he worked on brands including HP, Western Digital and Pfizer.
He replaces Mark Perkins, who moved to W last year, and is the most senior creative figure at the Engine-owned agency.
Quince was also previously a board director at Freuds, where he headed the digital practice. He also created the Itchy Guide series of youth city guides, which sold to EMAP in 2006.
MHP CEO Alex Bigg said: "I’m thrilled that Ruby has joined MHP at such an exciting time for the agency. Ruby has a track record of developing successful creative campaigns for well-known brands and I’m confident that he will bolster our creative power, helping us to deliver even bigger and more impactful campaigns for new and existing clients."
The news follows a number of appointments in the senior team at MHP under Bigg, who joined from Edelman in 2016.
These include former Edelman UK corporate and financial practice head Nick Barron, who joined as deputy CEO; former Bell Pottinger partners Andy Bloxham and Jamie Lyons to top public affairs and corporate roles; and Mike Robb, previously executive director at Cicero, as head of financial services.
Gemma Irvine was recently promoted to head of brand at MHP, succeeding Rachael Sansom, who left last Autumn.
MHP also announced changes to its health division in January, with practice head Rachel Rowson moving into a new role focused on health tech and her former position being taken by Kate Pogson.
In January, PRWeek named MHP as one of its seven UK PR agencies to watch in 2018.
- Click here to read PRWeek’s interview with Bigg on his plans to "turbo-charge" the agency