The remains of the Orphir Round Church (or Round Kirk), dedicated to Saint Nicholas, are located in Orphir Parish on the Mainland of Orkney, Scotland. It is thought to have been built by jarl (earl) Haakon Paulsson (earl from 1103 to 1123) as penance for murduring his cousin and co-ruler Magnus Erlendsson (later Saint Magnus) in the late 11th or early 12th century. According to the Orkneyinga saga, earl Haakon took sole power in 1117 after the killing of Magnus, and the round kirk was later rededicated to St Magnus. The saga refers to a "large drinking-hall" with a "magnificent church" nearby. The remains of the drinking hall, known as the Earl's Bu, can still be seen, as well as a later Norse horizontal watermill.
It is the oldest surviving round church in Scotland. The building's design was inspired by the Church of the Holy Sepulchre in Jerusalem. It consisted of an apse on the eastern side of its 6-metre (20 ft) wide circular nave. It consisted of a circular nave about six metres in diameter with a semicircular apse with a central window. The walls are one metre thick.
Almost the whole church survived until 1757, when most of it was demolished to provide stone for the new parish kirk, which has also now been demolished. Only the apse and a small segment of the round kirk's nave wall now survive. The site is now in the care of Historic Environment Scotland and is open to the public. The remains are protected as a scheduled monument.