Merlin studied at Cambridge University, where he was a scholar of Clare College. He received a triple First in his MA degree in the Biological Sciences, and a First with distinction in his MSci degree in the History and Philosophy of Science. He was awarded the University Lipton Prize for best performance in History and Philosophy of Science, the Clare College Godwin Prize for the Life Sciences, and the Clare College Greene Cup, awarded for academic excellence to one student a year. Following his masters degree, he received a Cambridge University scholarship for a PhD in Tropical Ecology and worked on mycorrhizal fungal networks in Panamanian tropical forests, based at the Smithsonian Tropical Research Institute, where he held a predoctoral Smithsonian Research Fellowship. He was awarded his PhD in June 2016. As well as his work in Panama, he has spent time doing research in labs in Lund (Sweden), Marburg (Germany), Cambridge, and London.

Merlin is a Research Associate at the Vrije University in Amsterdam and Oxford University, and the UK Policy Lead for the Fungi Foundation. He works closely with the Society for the Protection of Underground Networks, and is a core member of the More-Than-Human Life Project, which works to deepen and expand legal frameworks to better include the living world. He is the 2025 Distinguished Fellow at the Center for Human Rights & Global Justice at NYU, and co-launched the Fauna Flora Funga Initiative (together with the Fungi Foundation and NYU School of Law).

He is a pianist and piano accordionist, and is a member of the London-based Gentle Mystics. His publications are listed here.