The borough was the successor to two local authorities: the vestry of Stoke Newington parish in the County of London and the South Hornsey Urban District Council in Middlesex.

The union with Hackney was very unpopular with the inhabitants of Stoke Newington, and following unsuccessful attempts to end it in 1864, 1880 and 1890, the parish regained independence in 1894.

The exclaves of South Hornsey effectively cut off the south-eastern section of Stoke Newington from the rest of the parish.

The first two options were rejected due to the experience of "intolerable and interminable feuds" between the districts when they were previously "forced together", and because the First Lord of the Treasury, Arthur Balfour recognised that there was "great ill-feeling and mutual ill-will... between the inhabitants of the two districts";[4] it was therefore decided to merge the bulk of South Hornsey, with a population about 20,000, with Stoke Newington.

The commissioners realigned the boundary lines so that for the most part they ran down the centre of roads, railways or watercourses.

Stoke Newington's boundaries with the two neighbouring metropolitan boroughs within the County of London were as follows:[7] The long association with the dean and chapter of St Paul's Cathedral is represented by the red background and crossed swords.

The cross is from the arms of William Patten, first lord of the manor and rebuilder of the church of St Mary, in 1550.

These armorial devices were chosen to represent the union of Stoke Newington in the County of London and South Hornsey in Middlesex.

The crest was formed by a tree, recalling Stoke Newington's origin as a village in the Middlesex Forest.

Following the addition of most of South Hornsey and the boundary adjustments with Hackney and Islington, the area of the borough in 1901 was 863 acres (3.5 km2).