The Roman Catholic Diocese of Lancaster is a Roman Catholic diocese centred on Lancaster Cathedral in the city of Lancaster in Lancashire, England and as of 9th April 2018, the Bishop of Lancaster is Paul Swarbrick.
The Diocese is in the province of Liverpool. It extends along the west of England from the Ribble River in the south of Preston to the Scottish border, comprising the counties of Cumbria and much of Lancashire. The diocese has around 90 active priests, 50 permanent deacons, 12 secondary schools, over a hundred primary schools and a similar number of parishes.

The diocesan area is 1,100 sq miles. In 2004 the Catholic population of the diocese was 111,264 for a total of 1,050,000 inhabitants (10.6%). Areas in the diocese include the city of Preston; a city with an uncharacteristically high Catholic population – the highest anywhere in England & Wales.

The Cathedral Church of St Peter on Balmoral Road, Lancaster, is the diocesan cathedral and the seat of the Bishop of Lancaster. Completed in 1859 as a parish Church of the Archdiocese of Liverpool, and raised to the status of a cathedral upon the establishment of the diocese in 1924, St. Peter’s is a functioning parish. In addition, its grounds host numerous diocesan offices, including the Bishop’s Office, Finance Office and the Diocesan Youth Service. Central organisations of the diocese include the residential youth centre Castlerigg Manor, the Diocesan Youth Service, the Education Centre, Catholic Caring Services and others including the monthly diocesan newspaper, The Voice.