The Right Reverend St. John O'Sullivan (pronounced "sin-jin") (March 19, 1874 – July 22, 1933) was a Catholic priest who personally undertook the restoration of the old Mission San Juan Capistrano in California.
O'Sullivan was born in Louisville, Kentucky. From his given name and place of birth, it can be presumed that he was partially descended from the English Catholic settlers of Maryland who later helped to settle Western Kentucky. He then attended the University of Notre Dame in Indiana. While there he determined to become a priest, and was accepted by his home Diocese of Louisville. He enrolled in Saint Bernard's Seminary in Rochester, New York, to do his theological studies, graduating in 1904, when he was ordained by the Bishop of Louisville, William George McCloskey.
Within months of his ordination, O'Sullivan was diagnosed as suffering from tuberculosis, and advised that his prognosis was poor. He decided to seek a drier climate in order to cope better with the disease and, with his bishop's permission, moved to the American Southwest. He helped in various parishes in Texas and Arizona. In this way, he came to know the Rev. Alfred Quetu, the Catholic pastor of Prescott, Arizona. The pastor suggested that O'Sullivan might find the abandoned Mission San Juan Capistrano in California might provide him a place for him to exercise his ministry in a manner compatible with his health. O'Sullivan traveled to the Mission, where he fell in love with the site.