Katie Lee is leaving Lucky Generals as chief executive to join a mental wellbeing app called Clementine in the same role.
She departs the agency that she joined at the beginning of 2019 this week. Lee was Lucky Generals' first CEO and focused on running the UK office while the agency set up in New York.
Under Lee's leadership, the shop won the Zoopla account last year and managed to retain talent with just a 7% turnover rate in 2019, compared with the industry average of 31%.
She is also one of few leaders who have set up a miscarriage policy at an agency in a bid to bring taboo subjects into the open.
Before working at Lucky Generals, Lee was managing director of Y&R between July and September 2018 but was made redundant when the agency merged with VML to form VMLY&R.
Lee's advertising career also spans MD roles at Sunshine, Gravity Road and Leo Burnett, as well as stints at Bartle Bogle Hegarty, Saatchi & Saatchi and Collett Dickenson Pearce.
Helen Calcraft, co-founder of Lucky Generals, said: "Katie has been a highly energetic and much-loved General, and in particular, we honestly don't know how we would have navigated the pandemic without her kindness, wisdom and can-do attitude.
"So advertising's loss will be the mental-health arena's gain, and we are certain that Katie will be an inspirational and highly successful leader who will drive Clementine's wonderful mission to help millions of women reduce stress and build confidence.
"We will miss you, Katie, and we hope that we can get your business without a pitch!"
Clementine, which has 75,000 subscribers, who are based mainly in the UK, aims to expand globally after a £1m investment from Fortunis Capital. The app was founded by Kim Palmer, a former strategy director at Wunderman (now known as Wunderman Thompson), in 2017.
Lee said: "I've loved my advertising career to date, but the time has come for a pivot. Clementine combines entrepreneurship with the growing wellness trend and a really strong sense of purpose. Its time is now, and I want to capture this moment.
"While some brands layer on purpose, making a tangible, positive difference to people's lives is the reason that Clementine exists.
"It is not about 'this start-up could have me in a yacht on the Bahamas', it is about getting out of bed every day and genuinely being excited about what I am doing, making a tangible difference to women's lives."
Lucky Generals is yet to announce a new appointment.