Johnstone will join founders Peter Thomson and David Coates at UPP, which works on building and managing agency rosters for clients.
UPP launched last November with clients including Jazz FM and International Sports Events Consulting. It has an informal relationship with Publicis Groupe agencies and offers channel planning alongside agency relationship management.
During his 20-year career, Johnstone has experience of magazine brands including Wallpaper*, Loaded and Marie Claire. He worked in ad sales at Emap, Dennis Publishing and Ministry of Sound before joining IPC Ignite and then IPC Southbank.
Thomson said: "Richard is an amazing thinker, fantastic communicator and brand marketer. His practical knowledge of content creation, brand development and how media owners operate, will provide UPP and its clients with the insight and support needed to grow their businesses and create brilliant campaigns."
Johnstone said: "UPP provides clients with a structure, methodology and access to a roster of 20-plus globally famous agencies that will make marketing directors more effective than ever in delivering brilliant campaigns and results. I cannot wait to get started."