St John's Seminary was a Roman Catholic seminary located at Wonersh near Guildford in Surrey, in the Diocese of Arundel and Brighton, United Kingdom. St John's was the principal seminary for the Diocese of Arundel and Brighton and the Archdiocese of Southwark, and other dioceses to a greater or lesser extent, including Diocese of Plymouth, Portsmouth, East Anglia, Clifton, Menevia, the Archdiocese of Cardiff and the newly founded Ordinariate of Our Lady of Walsingham.
Established in 1891, in late 2020 it was announced that the seminary would close in mid-2021. The formal closure took place on 3 July 2021, the same day on which five of the former seminarians were ordained as deacons.The seminary served mainly the dioceses of the South of England, it also provided formation for students from dioceses further afield and for members of religious institutes. From 1985 it offered courses in theology for lay (external) students. These courses ran alongside the academic programme offered to students in formation. This programme was validated by St Mary's University, Twickenham, of which the seminary was an Associated Institution. The seminary was also a resource for local Church activities, and provided a venue for various groups including the formation programme for the Permanent Diaconate, as well as a centre of expertise in the work of formation and sacred science.
The seminary occupied a building listed Grade II on the National Heritage List for England.