Niall Sidney Harrison is a British medical writer and science fiction editor, critic and publisher.

He was a judge of the Arthur C. Clarke Award in 2006 and 2007 and Guest of Honour at Eastercon 2023.

[1] He is co-chair of the ACCORD Steering Committee, which is developing a guideline to improve the reporting of biomedical studies that use consensus methodologies.

Between 2007 and 2010, he was senior reviews editor for Strange Horizons; in 2010 he became editor-in-chief, a position he served in until stepping down in 2017.

[3] As a critic, his work has appeared in Interzone, Foundation and The New York Review of Science Fiction as well as Vector and Strange Horizons.