Sea Mills derives its name from a watermill just above the tidal limit of the River Trym, recorded first in 1411 as Semmille and in 1484 as Cemille.

[6] When the Bristol Port and Pier Railway Company standard gauge line (so named because Avonmouth as a port did not then exist) was opened beside the Avon in 1865, from Hotwells to a new deep water pier at Avonmouth, the station built on the south side of the Trym to serve the mansions and villas of the wealthy districts of Stoke Bishop and Sneyd Park was therefore called Sea Mills.

In the 1820s it was proposed and generally accepted that this was the site of the port of Abona (Avon),[11] linking Silchester and Bath with Venta Silurum (Caerwent) in Wales, on Route 14 of the 3rd-century Antonine Itinerary’s Britannia section.

[12] Piecemeal archaeological excavations have since found evidence of the street pattern, buildings within the small Roman town and cemeteries outside it.

[13] The Sea Mills area was entirely rural until the British government launched a heavily subsidised scheme after the First World War to build "homes fit for heroes".

To ensure rapid implementation, however, that April Bristol Corporation had bought two farms on the southern edge of the King’s Weston Estate, on which to build a low-density garden suburb for the working classes to standards recommended in the Tudor Walters Report that the legislation was based upon.

[16] Addison's Oak still stands on Sea Mills Square, actually an elongated semicircle at the centre of the garden suburb, and was a runner-up in the 2019 Woodland Trust tree of the year competition.

[17] "The Square" was to have been a quadrangle, bisected by Shirehampton Road, but the initial plan was modified to follow a celebrated design by the chief architect of the national housing scheme, Raymond Unwin, who had ultimate responsibility for approving the Sea Mills layout.

In the course of development, the plan was further modified to be less dense and formal, with fewer right-angles and squares and more open spaces, to follow contour lines, and to create a more coherent northern framework.

Its lasting legacy is a mini-museum situated in a K6 phone box on Sea Mills Square,[24] which was renovated by local volunteers as part of the project.

Before the current Sea Mills Methodist Church building was built their fledgling congregation worshipped in a wooden hut on the same site.

In view of its early date and integrity as a garden suburb "fit for heroes", in 1981, Sea Mills was one of the first housing estates in the country to be designated as a conservation area.

[34] Initially, the designation extended to the north only as far as Sylvan Way (a council ward boundary since 2015); to the east to include the part of the Trym valley bordering the garden suburb; to the west the River Avon adjacent to the rest of the conservation area and land between it and the Portway; and to the south the old Sea Mills harbour and land immediately behind it: Sea Mills Station, adjacent late Victorian and 1950s signal stations on the Avon, Roman ruins at the entrance of Roman Way, allotments opposite the station, and 1940s prefabricated houses on Hadrians Close (since demolished but mostly not later built over).

[35] The Sea Mills conservation area was extended in 2008 to include the rest of the garden suburb up to Westbury Lane, including the north side of the lane, which was not part of the garden suburb but forms "an essential ‘setting area’ … which continues [its] verdant, spacious and low density character".

This includes: Haig Close, a small pre-war estate of almshouses originally built for disabled ex-servicemen and their families by Bristol Corporation on land given by Mr Napier Miles; a large former public house built in 1938, now the Red Bus Nursery and Pre-School Coombe Dingle; and a small 1930s parade of shops.

Also included are houses privately built by the King’s Weston Estate in the 1930s, as part of the garden suburb, on land noted in the 1920 plan as being intended for smallholdings.

There are frequent bus services on Shirehampton Road, Westbury Lane, Sylvan Way and the Portway to much of Bristol, including the city centre, Avonmouth, Westbury-on-Trym, Southmead and Cribbs Causeway.

The Portway (A4) trunk road passes along the south-western edge of Sea Mills and links central Bristol with its port at Avonmouth.