John Magnier (born 10 February 1948; also known as "The Boss") is an Irish business magnate.
He is Ireland's leading thoroughbred stud owner and has extensive business interests outside the horse-breeding industry.
Magnier has also been a Senator in the upper house of the Irish Parliament, Seanad Éireann.
He is based at Coolmore Stud at Fethard in County Tipperary, considered one of the world's pre-eminent stallion stations, and a nursery of thoroughbreds.