After political moves, and potential engineering difficulties with hills south of Eastwood station in the 1930s, the terminus was changed to Epping, where the line became known as the "Epping-St Leonards Railway".

An original proposal to run from Westmead to St Leonards, via Epping was considered, but in 1998 the Parramatta Rail Link was announced as part of the NSW Government's Action for Transport 2010 plan.

This proposal included optional stations at Delhi Road and UTS Kuring-gai and would be served by eight services an hour.

In August 2003, the NSW Transport Minister, Michael Costa, announced that the Epping-Parramatta section would be postponed indefinitely.

The government later announced the construction of a passing loop as part of the Rail Clearways Program on the Carlingford line, which would have allowed a half-hourly frequency all day,[6] however this project was cancelled in November 2008.

Thiess and Hochtief delivered the project as a joint venture which included the design and construction of a driven railway and four fully mined stations.

[12] On 23 October 2008 it was also confirmed during testing that sound levels on the train were 90 decibels, as loud as a 737 plane coming into land.

[13] In July 2009 it was reported that drivers were being restricted to two return shuttle runs through the tunnel before taking a break as well being instructed to keep the lights on in the driver's cabin and lower the side window blinds in order to avoid a possible stroboscopic effect caused by the tunnel lighting, with claims it may have caused headaches, dizziness, fatigue and nausea.

[15][16] The launch was moved from 22 February due to a National Day of Mourning for the victims of Victoria's Black Saturday bushfires.

[18] Initially passengers could use a blue Complementary Pass, or buy a ticket to either Chatswood or Epping if coming from outside the new link.

These were the newest trains in the fleet and are intended for longer journeys out of the Sydney basin, but were used on the ECRL due to the steepness and noisiness of the tunnel.

Other types maintained at Hornsby Maintenance Depot were not used during the shuttle phase, though tests with K sets proved successful.

[19] The line was coloured black on CityRail maps and publicity materials during the shuttle period, which ended on 11 October 2009 when a new timetable was introduced.

On 11 August 2010, Prime Minister Julia Gillard announced $2.1 billion in funding for the Epping to Parramatta Rail Link with $520 million to be contributed by the NSW Government.

In 2012, it was announced that the project would adopt different technology from Sydney's existing rail system, instead running single-deck automated trains with platform screen doors.

[25] The North West Rail Link project – renamed Sydney Metro Northwest – involved the conversion of the existing Epping to Chatswood section to form part of the new Sydney Metro network and allow the new, automated line to run as a shuttle between Tallawong and Chatswood.