The diocese of London was first established in the Roman period, the first known bishop being Bishop Resitiutus who attended a Council in Arles in 314. London reverted to paganism following the Saxon invasions and the diocese was reconstituted in 604 with the first Saint Paul's as its Cathedral. The medieval diocese continued its jurisdiction over the area established in the 7th century: namely the City of London and the ancient counties of Essex and Middlesex and the greater part of Hertfordshire, and diocese lay entirely north of the Thames River.
The area served by the diocese remained unchanged until the 19th century, apart from a short period between 1540, when the diocese of Westminster, founded by Henry VIII, was taken out of the diocese of London covering Westminster, the county of Middlesex with the exception of Fulham, and 1550 when the appointed Bishop Thirlby resigned and the bishopric reverted back to London.
The administration of the diocese was originally split into the Archdeaconry of London and Archdeaconry of Middlesex. In 1708 there were 5 churches and chapels subject to the archdeacon of London, 52 subject to the archdeacon of Middlesex, 14 subject to the bishop directly and 4 subject to the Archbishop of Canterbury and outside the jurisdiction of the diocese of London.
The growth of population in the 19th and 20th centuries demanded rearrangements of the boundaries of the diocese. Up until 1845 the diocese comprised of most parishes in Middlesex except part of Stanwell which lay in the diocese of Oxford, the City of London parishes excluding the thirteen parishes in the peculiar of the Arches, a substantial number of parishes in Hertfordshire and four parishes in Buckinghamshire namely Aston Abbots, Grandborough, Little Horwood, and Winslow.
The abolition of the Peculiar jurisdictions of the Archbishop of Canterbury the ecclesiastical units within the Middlesex area which were exempt from the administrative control of the diocese in 1845 added the thirteen parishes in the City of London, some parishes in Middlesex, and those in the Deanery of Croydon in the ancient county of Surrey Barnes, Mortlake, Newington, Putney, Walworth and Wimbledon. The diocese retained nine Essex parishes Barking, Chingford, East and West Ham, Little Ilford, Low Leyton, Walthamstow, Wanstead and Woodford. The rest of Essex was temporarily transferred to the see of Rochester and the parishes in Hertfordshire and Buckinghamshire were removed from the diocese. At the same time parishes in the ancient county of Kent Charlton, Deptford, Eltham, Greenwich, Lee, Lewisham, Plumstead and Woolwich just south of the Thames were brought into the diocese.
Under the London Diocese Act 1863 and Diocese of Saint Albans Act 1875, provisions were made for the removal of Essex, Kent and Surrey parishes. In 1877 Surrey and Kent parishes were transferred to the diocese of Rochester, and then Surrey parishes to the diocese of Southwark in 1905.
The appointment of Suffragan bishops was also revived in the 19th century with officials holding the titles of Bishop of Stepney, Islington and Kensington.
Further reorganisations were designed to link the ecclesiastical boundaries with that of county administration. In 1912 the Archdeaconry of Hampstead was carved out of the Archdeaconry of Middlesex. In 1914 the diocese had 6 rural deaneries of Ealing, Hammersmith, Hampton, Hornsey, Uxbridge and Willesden. In 1951 parishes East of the City of London formed the Archdeaconry of Hackney. By 1964 the diocese of London consisted of the archdeaconries of London, Middlesex, Hampstead and Hackney with a total of 28 deaneries and 500 parishes.
In 2001 the diocese was made up of five areas, Edmonton, Kensington, London, Stepney and Willesden, 4 of which had an Area Bishop, to whom the Bishop of London delegated responsibilities. It covered 277 square miles and 17 boroughs of Greater London north of the Thames, from Staines in the West to the Isle of Dogs in the East serving a population of 3.5 million people.