Donna Macmillan studied Biomolecular and Medicinal Chemistry at the University of Strathclyde in Glasgow where she remained to complete a PhD in organic medicinal chemistry, focused on the development of novel drugs for schizophrenia. In 2013, Donna joined Lhasa Limited where she specialized in knowledge-based expert systems and QSARs across several endpoints, including mutagenicity and skin sensitisation.

Transitioning to Humane Society International in 2021 as a Principal Strategist in Regulatory Science within the Research and Toxicology department (later promoted to Senior Principal Strategist), Donna worked to advance a paradigm shift from traditional toxicology to non-animal approaches for chemical safety assessment. In late 2023, Donna assumed the role of Director, Outreach and Capacity Building at the International Collaboration on Cosmetics Safety (ICCS). In this role, she leads efforts to leverage scientific advancements in cosmetics safety.