Planning, construction, and opening
The Mass Rapid Transit (MRT) system was conceptualised in a 1971 study conducted by the Singapore Government and the United Nations Development Programme. The study – which assessed land-use transportation needs – concluded that Singapore would need a rail transit system by 1992. Further studies and debates on the feasibility of building a rapid transit system took place from 1972 to 1980, with Eunos station appearing in initial plans by May 1982. Eunos was proposed to be constructed as part of the 32.6 kilometres (20.3 mi) East–West Line (EWL), which was to have 22 stations and run from Jurong West to Bedok. On 30 May 1982, communications minister Ong Teng Cheong confirmed that the government approved construction of the MRT; the system was planned to be constructed in three phases, with Eunos part of "Phase II", which was 40 km (25 mi) long and composed of 22 stations. Phase II would be constructed in different sections, with Eunos specifically part of "Phase IIA", which consisted of 13 stations from City Hall to Pasir Ris. Stations under Phase II were planned to start construction while Phase I stations are under construction to ensure that the MRT would be fully open by the early 1990s.
From May to June 1984, the Mass Rapid Transit Corporation (MRTC) called for the prequalification of consultants to design the civil, architectural, and structural works for Phase IIA stations. Ten companies were shortlisted by July. The MRTC awarded the contract to an American–Singapore consortium between De Leuw Cather, Wilbur Smith & Associates, Skidmore Owings Merrill, and Singaporean firm RSP Architects in October for S$11.5 million (1984) (US$5.39 million). The Straits Times reported in November that Phase II was ahead of schedule by two years due to the successful timing for Phase I. By May 1985, there were seven tenderers that prequalified for Contract 303, which initially detailed the construction of Paya Lebar station and a viaduct from Paya Lebar to Eunos. Ultimately, the contract was awarded to a Japanese–Singaporean joint venture between Okumura Corporation [jp] and Oh Teck Thye, which had the lowest price among five other tenderers, for S$60 million (1985) (US$27.27 million) in December 1985. Okumura had a 60% interest in the contract whilst Oh Teck Thye had 40%. By then, the contract also included the construction of Eunos and viaducts to Kembangan station.
Work on Contract 303 began in December 1985, and construction for Eunos began in January 1986; the project was expected to be completed by December 1988. By February 1986, 41% of the contract had been completed. In July, Swiss–Singaporean company VSL Singapore was awarded the subcontract for the supply of post-tensioned cables and precast beams for the station's viaducts. The joint venture between Okumura and Oh Teck Thye was terminated on 30 December 1986, after which the former undertaking all the responsibilities of Contract 303. Oh Teck Thye owed S$3 million (1987) (US$1.42 million) to the United Overseas Bank (UOB) and was placed under receivership of Peat Marwick Mitchell when it failed to repay its debts. Meanwhile, Okumura requested permission to take over Oh Teck Thye's part of the contract. Soon Neo Lim of The Business Times described it as "the first case of a joint-venture split in the MRT Project". By December 1987, Eunos was expected to be completed by September 1989.
Although stations in the City Hall–Changi stretch were initially expected to commence operations by December 1989, The Straits Times reported in February 1989 that Phase IIA was ahead of schedule and could commence operations in the last quarter of the year. Civil works for Eunos were fully completed by April 1989 and from August, test runs were conducted on the City Hall–Tanah Merah stretch to check the trains and tracks. By then, communications minister Yeo Ning Hong announced that stations within the City Hall–Tanah Merah stretch would open on 18 November, though by September, the opening date was moved ahead two weeks as the test runs were ahead of schedule. Eunos, along with 9 other stations between Marina Bay and Tanah Merah, opened on 4 November 1989.
After opening
In February 1996, a flight of stairs from the station's terrace to the street level underwent repairs after it had sunk into the ground. The difference between the concrete of the terrace and the soft soil of the ground resulted in a 40-centimetre (16 in) drop, which posed a risk for elderly commuters and young children. In August 2006, a letter written by a member of the public was sent to Today, who observed that the stairs at the station's south front exit "[led] to nowhere". The author also observed that a set of steps connected to a ramp near Eunos Food Centre at the east side of the station "assumes the wheelchair bound can suddenly get up and walk the [steps connected to the ramp]". SMRT Corporation clarified that the first set of stairs was meant to connect a carpark to the station, whilst the ramp was originally not meant for wheelchair users. It added that works were underway to fix the first set of stairs, which was uneven due to sinking into the ground, and to remove the ramp's stairs to make it wheelchair-accessible.
On 5 December 2000 at 8:15 am, a man fell on the eastbound track just as a train was entering the station. The train struck the man, trapping him between two of its cabins. He was rescued by emergency forces but died an hour later. Following an increase in track intrusions, the Land Transport Authority (LTA) and SMRT decided to install platform screen doors at all elevated MRT stations. After several successful tests at different stations, works to install half-height platform screen doors were expected to start in 2010; they were installed at Eunos by August 2011.
