Otaki is essentially a Troup Vintage station without the external embellishments. It is a gabled rectangular structure with a verandah and clad with rusticated weatherboards. It has a corrugated-iron roof on both the main building, capped by three chimneys, and the verandah. There is a brick wall between what was the refreshment room to the south and the building proper. Both elevations have double-hung sash windows (boarded up on the platform side) and four-panelled doors. The verandah is supported by wrought-iron (originally railway-iron) posts, which together with the fashioned timber valances at both ends of the verandah add a decorative element to the platform elevation. Interior modifications have been confined to opening-out and the conversion of internal spaces such as the former Post Office and public offices. Many internal features such as the architraves, windows and surrounds, and fireplaces remain
The privately owned Wellington and Manawatu Railway opened in 1886 and it is probable that the first Otaki station building dated from that time. On 24 July 1910, two years after the government bought the railway, the building was destroyed by fire. All that was left standing were the iron posts from the verandah, which had only recently been erected. The station was rebuilt at a cost of £1150 - £150 was contributed by the Post and Telegraph Department, which kept an office in the station until 1951. The design was intended to follow that of the nearby Levin, with a particular requirement being a brick wall between the refreshment room and the offices. Much of the building has had different uses. In 1939 the kitchen was used by signal staff; in 1957 the vacant Post Office became the signal room and the previous room was taken over by railway electricians. In 1963 the signal room became a staff amenity room. Otaki became a special purpose station in 1986, with ballast traffic from the pit at the Otaki River being the major local traffic.