Mason-Pearson, who spent almost six years at Spider PR, launched Kitten & Shark this month, with several clients and one staff member transferring from her mother's agency.
According to Mason-Pearson, Kitten & Shark will work with start-ups "eager to build awareness" and established lifestyle brands "needing a revitalising and a fresh outlook".
Clients include gastropub and hotel chain Cubitt House and Spanish health & wellbeing retreat, Healthouse Las Dunas.
Mason-Pearson said: "We build reputations for brands, we successfully launch products, we promote places, we profile people... but most of all we work with our clients to identify what they consider a successful PR campaign looks like, and then we deliver it."
While at Spider, Mason-Pearson helped launch the agency's luxury lifestyle division. She will continue to work within the agency's corporate division and social media teams on a consultancy basis.
Prior to joining Spider as director in 2012, Mason-Pearson was head of travel at PR firm The Lifestyle Agency. Before this, she was account manager at global comms group PRCO.