Hearts & Science UK Names Tessa LeGassick as Chief Planning Officer

Jan. 13, 2026

Hearts & Science UK has announced the promotion of Tessa LeGassick. She joins the exco in the newly created role of Chief Planning Officer.

As one of the agency’s founding members in 2017, LeGassick has been instrumental in shaping the agency’s strategy. She established Hearts’ Connections Planning department and transformed it into a core discipline across all clients. 

The establishment of the new chief planning officer role will allow her to further develop the department and build on the agency’s strong growth trajectory. Hearts was recently crowned the fastest-growing media agency having seen YoY billings growth +25%, YoY headcount growing 70%, and an 187% uplift in client work award wins year-on-year.  

LeGassick has achieved widespread industry recognition during her tenure and was named Media Planning Leader of the Year by Campaign this year. She is credited with pioneering new standards in attention-led and inclusive planning, as well as co-authoring the agency’s Conscious Inclusion framework.

Commenting on her promotion, Garrett O’Reilly, UK CEO, Hearts & Science, said:

“Tess has been instrumental in the development of our planning team. It is in no small part down to her that Hearts has achieved a true mastery of the planning craft - as is made abundantly clear by our successes both in new business and in award-winning work. Her impact on growth, culture, and client success at Hearts has been extraordinary and this promotion is a recognition of her talent. In her new role, I’ve no doubt that Tess will continue to redefine what great work looks like both within the agency and for the wider industry.”

 

LeGassick, who will report directly to O’Reilly, added:

“Connections planning contributes to what gives Hearts its edge. I’m proud to have helped build a discipline that blends data, creativity and the craft of planning in a way that drives real effectiveness. This next chapter is about continuing to lead a team that brings sharp, future-facing thinking to client challenges - and evolving the excellence of our planning processes and products as we continue to grow. Having Acxiom as part of our tech stack means we’ll also collaborate seamlessly across Hearts departments and other Omnicom Media agencies”

 

LeGassick has helped build several proprietary frameworks that have been vital to Hearts’ success, including the Velocity planning model (Decode, Recode, Activate, Review), turning the agencies industries award winning Category Entry Points approach into media planning innovation, and Planning Foundations - a training programme for junior planners. 

She has also played a key role in defining the agency’s culture, mentoring emerging talent, supporting OMG’s Working Parents & Carers group, and sharing her latest thinking at IPA industry events.