The estate is built in the grounds of the former family seat of the Rushout family, the Barons Northwick. The Northwick Park mansion, now divided into residential accommodation, is a Grade 1 listed building. It passed out of the Rushout family in 1912, when it was inherited by the then Lady Northwick's grandson, George Spencer-Churchill.
Because the area was under the authority of the Bishops of Worcester, it was actually a small enclave of the county of Worcestershire surrounded by Gloucestershire - and is shown that way on all maps prior to 1931, when such enclaves were rationalised.
The estate includes the site of the former hamlet of Northwick, which is listed in the Domesday Book. During the Second World War, Northwick Park was an American field hospital. It became a camp for Polish displaced persons until the 1960s.