Originally built to serve the mansions and villas of the wealthy districts of Stoke Bishop and Sneyd Park, the station had a single platform.

After a tunnel was driven under The Downs, passenger services connected it to the wider rail network in the 1880s via the Clifton Extension Railway.

Passenger numbers greatly increased, particularly after Sea Mills Garden Suburb was built by Bristol Corporation on the opposite bank of the River Trym in the 1920s, and the remaining farmland in Stoke Bishop and Sneyd Park was infilled with private suburban housing throughout the inter-war period.

The surrounding area is mostly residential, with allotments to the west and a small football ground (Bristol Manor Farm FC) to the north.

The route was 4 ft 8+1⁄2 in (1,435 mm) standard gauge single track, with Sea Mills initially the first station along the line, 2 miles 01 chain (3.2 km) from the southern terminus at Hotwells.

With no prospect of a proper dock being funded without a connection to the national rail network, the Clifton Extension Railway (CER) was approved.

[2][18] The link opened in 1877, but only for goods trains: Colonel William Yolland, the chief inspector of British railways, considered the platforms at Sea Mills to be too short for passenger interchange, as they were 250 feet (76 m) shorter than at any station on the CER.

Rather than build a new interchange station at Sneyd Park Junction, the platforms at Sea Mills were extended to 300 feet (91 m) at the expense of the BPRP.

[18] From 1 September 1885, when passenger services along the link finally started, the Great Western offered six trains per day each direction between Avonmouth and Bristol Temple Meads.

[6] Increased levels of traffic saw the line through Sea Mills doubled in the early 1900s,[19] and the opportunity was taken to rebuild the station.

A station building was constructed on the original platform in a domestic style, with an arched terracotta entrance, spar-covered walls and a high-pitched tiled roof.

[18] After the First World War, construction of the Bristol Portway along the Avon Gorge necessitated the closure of the line from Sneyd Park Junction to Hotwells, with trains along it ceasing on 3 July 1922.

To compensate for the loss of service, the Great Western provided an additional four trains daily towards Bristol and six toward Avonmouth.

A year later in 1963, the Beeching report suggested the complete withdrawal of services along the line, but ultimately only those beyond Severn Beach or via Henbury were withdrawn.

From 17 July 1967 all staffing was withdrawn from stations along the line, including Sea Mills, with tickets issued by the train guard.

[18] British Rail was split into business-led sectors in the 1980s, at which time operations at Sea Mills passed to Regional Railways.

[19][20] When the railway was privatised in 1997, local services were franchised to Wales & West,[21] which was succeeded by Wessex Trains, an arm of National Express, in 2001.

[22] Following action by Friends of Severn Beach Railway (FOSBR) and a string of protests, services had increased to 10 per day in each direction by 2005,[6] with Bristol City Council providing a subsidy to Wessex Trains.

[48][49] The enhancement scheme was given the go-ahead in July 2012 as part of the City Deal, whereby local councils would be given greater control over money by the government.

[50] There are also calls for the reopening of the Henbury Loop Line, which could allow a direct service from Sea Mills to Bristol Parkway via Avonmouth.

[52][53] There are also calls for the second platform at Sea Mills to be reinstated as a passing loop or as part of a restoration of the whole line to double track.