Zarnie is an internationally recognised researcher in digital health, implementation science, and cancer prevention. Her work uses innovative methods to address real-world challenges to widespread use of interventions / services that improve population health. She has published more than 60 peer-reviewed publications and has secured over £10.6 million in research income as lead, co-lead, or co-applicant on multicentre project grants. Zarnie had been awarded five competitive personal studentships / fellowships that have supported her research career to-date.

Her current programme of research is funded through a prestigious Cancer Research UK Fellowship (2024–2030), which focuses on optimising the uptake of weight-management interventions through use of digital technologies. She sits on the NIHR i4i Product Development Award Committee and the CRUK Bridge to Academic Leadership Panel. She co-leads the UEA Health and Social Care Partner group Changing Behaviour and Implementing Best Practice and is a visiting associate professor at UCL.

Zarnie has made significant contributions to capacity-building in implementation science. She designed and leads the multi-institutional postgraduate module An Introduction to Implementation Science, also delivered as an internationally marketed short-course. She was a key contributor to the ImpRes tool and guide for designing implementation research and the ImpResPAC appraisal criteria. Her systematic review of implementation outcome instruments informed the creation of the Implementation Outcome Repository, an openly accessible online resource supporting researchers worldwide in identifying and applying validated measures.