The Diocese of Brentwood (Latin: Dioecesis Brentvoodensis) is a Latin Church diocese of the Catholic church in England.

The diocese is a suffragan of the Catholic Archdiocese of Westminster.

The diocese covers the traditional county of Essex, an area of 3,959 km2 comprising the non-metropolitan County of Essex, the unitary authorities of Southend-on-Sea and Thurrock, and the London boroughs of Barking & Dagenham, Havering, Newham, Redbridge and Waltham Forest, matching Essex's historic boundaries and the Anglican Diocese of Chelmsford.

The see is in the town of Brentwood where the seat is located at the Cathedral Church of Saint Mary and Saint Helen.

The diocese was erected on 20 July 1917 from the Archdiocese of Westminster.