His family emigrated to New Zealand when he was young and he was schooled in Christchurch. He studied medicine at the University of Otago, New Zealand, returning to Scotland to complete his degree. He graduated from the University of Edinburgh with an MB in 1896. From 1898 to 1899 he was President of the Royal Medical Society. He received his MD in 1899 with a gold medal from the University of Edinburgh.
From 1908 until 1948 he held the Chandos Chair of Medicine and Physiology at the Bute Medical School, at the University of St Andrews, Scotland, during which time he described what are now known as Herring bodies, in 1908. He also carried out work on insulin, funded by the Medical Research Council. He was elected a Fellow of the Royal Society of Edinburgh in 1916, his proposers being Edward Albert Sharpey-Schafer, Sir James Walker, Cargill Gilston Knott, and James Hartley Ashworth. In the same year he was elected a Fellow of the Royal College of Physicians of Edinburgh. He served as Vice-President of the Royal Society of Edinburgh from 1934 to 1937.
He was awarded the honorary LLD by the University of St Andrews.
- The Spinal Origin of the Cervical Sympathetic Nerve (1903)
He married Mary Marshall Callender on 7 April 1905. They had four children.
- "Herring, Percy Theodore, (1872 - 24 Oct. 1967), Professor Emeritus, St Andrews University | WHO'S WHO & WHO WAS WHO". www.ukwhoswho.com. doi:10.1093/ww/9780199540884.013.u57192. Retrieved 27 January 2019.
- Herring, Percy Theodore. "Malpighian bodies of the kidney: a study on their development, comparative anatomy, and pathology". Edinburgh Research Archive. Retrieved 25 April 2017.
- Biographical Index of Former Fellows of the Royal Society of Edinburgh 1783 – 2002 (PDF). The Royal Society of Edinburgh. July 2006. ISBN 0 902 198 84 X.