After the government's decision to go ahead with the project at an estimated cost of S$5 billion, its alignment and stations were finalised in 1996 and construction began the year after.

The Mass Rapid Transit Corporation (MRTC) first proposed an additional MRT line serving the northeastern areas of Punggol and Jalan Kayu in September 1984.

[9] In its preliminary studies, the Communications Ministry concluded that existing roads would be inadequate for projected traffic into housing estates set to be built in the 21st century.

[10] In December of that year, a British consultancy team consisting of Sir William Halcrow and Partners, Merz & McLellan and London Transport International was appointed by the MRTC to look into possible routes for the line.

[15] Although the government approved the NEL "in principle" in January 1989, Communications Minister Yeo Ning Hong said that the line's construction was dependent on development in the northeast.

According to Yeo's successor, Mah Bow Tan, there were firmer plans for development around the Woodlands extension,[18] unlike in the northeast, where the low population meant that the NEL would not be as cost-effective.

[19] The four Members of Parliament (MPs) for the northeast called for the line to be built sooner, saying that there would be sufficient demand (given the area's population) and it would relieve traffic congestion.

The ministry recommended the construction of the NEL to the Cabinet, citing "wider benefits" such as reduced travelling time and reliance on cars.

Mah, engaging with grassroots leaders in October 1995, said that residents would have to be prepared to pay higher fares on the NEL to cover the line's cost and initial losses.

[22][23] A white paper released on 2 January 1996 said that the NEL would be built earlier to address congestion in the northeast corridor, which would also be relieved by express bus service.

[27] Many residents and politicians welcomed the announcement, since the line was expected to relieve traffic congestion, improve transport in the northeast and stimulate development around the stations.

[34][35] On 20 May 1999, SBS Transit (then Singapore Bus Service) was appointed to operate the line along with the Sengkang and Punggol LRT system.

[41] At the Outram Park station, an arched roof of cement-filled steel pipes was laid underneath the EWL tunnels to minimise movement.

[54] However, the Land Transport Authority (LTA) said in September 2002 that the line might be opened in April 2003 to allow sufficient time for testing.

[56] The NEL's opening was delayed until June due to a glitch in the signalling system, however, with tests briefly handed over to the LTA.

[58] Except for two stations (Buangkok and Woodleigh),[59] the NEL began operations on 20 June 2003 and was attended by Prime Minister Goh Chok Tong.

[68] Residents around the line were upset by the sudden decision to keep Buangkok station closed, since they had been assured by MPs and grassroots leaders that it would be opened.

[69][70] The government initially stood by SBS Transit's decision to keep the station closed, planning to open it in 2006 when more residential flats would be in the area.

[83] SBS Transit, after saying that it was still "too early to draw a conclusion" about ridership,[82] remained committed to keeping the station open to serve future developments nearby.

[89][90] On 17 January 2013, transport minister Lui Tuck Yew announced a one-station extension of the NEL to serve upcoming developments in Punggol North.

[1] The NEL's rolling stock has six-car electric multiple unit (EMU) trains, with four doors per side on each carriage, and can accommodate up to 1,920 passengers per trainset.

[121] An additional 18 second-generation Alstom Metropolis C751C trains, an updated version of the C751A,[124] were delivered to Singapore beginning in July 2014[125][126] and were built in Shanghai between 2014 and 2016.

[135] In an emergency when the train is stopped, the doors on both sides can be opened easily without electricity and ramps lower for passenger evacuation in the tunnels.

[153] Its construction allowed the LTA to explore, integrate and implement new and existing technology as part of its vision of a fully-automated system.

[158] In addition to assisting passengers and checking and topping up their fare cards, the PSC staff monitors and controls the functions of connecting tunnels and communicates with the OCC at the depot.

In addition to escalators, Dhoby Ghaut is the first MRT station with a set of 55-metre (180 ft) travellators which link the NEL and NSL platforms.

Consisting of tiles with raised rounded or elongated studs, the system intends to guide visually-impaired commuters through a station on a dedicated route from entrance to platforms.

[179] Exit A of the Chinatown station has a transparent pavilion-style roof, which allows natural light and provides an unobstructed view of the shophouses along Pagoda Street.

[184] The network's first such integration of an MRT station with a commercial development,[183][185] it permits more efficient land use and improves access to public transport.

[195][196] Covering 320 metres (350 yards) along Punggol Central to accommodate bus stops, taxi stands and passenger drop-off points along the road, the station is the NEL's longest.