The station was opened on 8 January 1907. It was initially a single-track station with a loop containing the racecourse platform, which served the recently opened
Trentham Racecourse. Double track reached Trentham in June 1955, with electrification following in September. Between 1955 and 2021, the
double-tracking of the
Wairarapa Line ended just north of Trentham station, with the line becoming
single track as it continued north. However, in normal operation, southbound trains used the Ararino Street (western) platform and switched over to the down line south of the station. The Racecourse Road (eastern) platform was only used during race days and for other special occasions that occurred at the adjacent
Trentham Racecourse. The 20102035 Regional Rail Plan (RRP) had proposed duplicating the track between Trentham and Upper Hutt in the 20112012 year, but duplicating the track only commenced as part of the 2020-2021 Wellington Metro Rail Upgrade. As part of the upgrade, the low platforms were raised and the east "racecourse side" platform was replaced with one further west to increase clearance between the two main lines. A new subway was built to connect the two platforms, and a new station building similar to the
Redwood station building was added to the new eastern platform. The new platforms came into operation on 15 November 2021, with services stopping at Trentham generally using the Ararino Street (western) platform if travelling to Upper Hutt and the Racecourse Road (eastern) platform if travelling to Wellington. Services not stopping at Trentham (e.g. freight services and the
Wairarapa Connection) may use either track, as the new double-track between Trentham and Upper Hutt is signalled for bi-directional running. Trentham was originally controlled from its own signal box on the main platform. Following double-tracking of the line to Trentham, the southern crossover points (number 18, now 1) and the associated signals protecting the crossover and the single line north could be controlled from the signal box at Upper Hutt, requiring the Trentham signal box only to be used on race days to operate the other crossovers and signals. On 6 February 2007, the Trentham and Upper Hutt signal boxes were decommissioned and control of both stations was moved to Train Control in central Wellington, and all crossovers and signals were renumbered. There was a set of sidings in the
Trentham Army Camp from 1941 to 1954, used for freight and for troop trains, with a shunting locomotive owned by the Army. Most of the track were removed in the 1970s. The siding was 0.53 km from Trentham Railway Station and 0.63 km from
Heretaunga Railway Station. ==Accidents==