Pahiatua is timber-framed, with lapped weatherboards and a squat, gabled, aluminium-clad roof. It has a cantilevered verandah to the platform elevation and a porch to the road elevation. The interior consists of a series of interconnected rooms, well-lit by numerous windows and with external access. The general office is reached from the main lobby. Some rooms have lost their purpose, as staff were reduced and eventually removed.
The first Pahiatua station building, a Vogel Gable design, was completed in 1897 when the Wairarapa Line opened. Numerous additions and modifications were made to accommodate changing needs. In 1957 complaints began to be made about the state of the building, and major alterations were planned. In 1963 Railways agreed that rebuilding was more appropriate and it was planned for 1967, but it was not until 1969 that plans were prepared and Treasury authorised £22,000 for the work. Work began in January 1970 and was finished on 17 March 1971. A drop in traffic levels by the early 1980s and the withdrawal of passenger services in the late 1980s led to rationalisation, to the point where only excursion passengers use the station. The freight yard is used by a railway heritage group and for main line operating purposes.