Built by EDi Rail between 2002 and 2005, the first sets initially entered service under the CityRail brand on 1 July 2002 after short delays due to electrical defects.

While the Millennium train concept is an evolution of the Tangara concept (manufactured by A Goninan & Co), the Millennium train introduced new features such as internal electronic destination indicators, automated digital voice announcements for upcoming stops, a return to reversible seating, surveillance cameras, wider stairways, a new safety yellow colour scheme, and push-button opened internal doors.

The Millennium Train also introduced crumple zones to absorb impact in a collision.

These allow passengers to manually open the doors in an emergency, as recommended in the report for the Waterfall rail accident.

The initial order signed in October 1998 was for 81 carriages, in December 2002 an option was taken up for an additional 60.

The Millennium trains were withdrawn from service in April 2003 while the problems were being rectified and a full audit was carried out.

As of the new timetable since 20 October 2024, M Sets now run 8-car services on the T2 Leppington & Inner West, T3 Liverpool & Inner West, T5 Cumberland and T8 Airport & South lines, while also running 4-car services T5 Cumberland, T6 Lidcombe & Bankstown and T7 Olympic Park lines.