[4] Mälartåg operates a regional train network consisting of five lines, covering a total length of 1,060 km and serving 44 stations.

In 1995, the company signed an agreement with SJ (Swedish State Railways) to operate regional train services in the area, leading to the formation of Trafik i Mälardalen AB.

[8] In December 2013, six public transport authorities in Mälardalen had already reached an agreement to develop train services in eastern Sweden.

[11] The decision to expand services led to the introduction of Mälartåg, which began operations in conjunction with the Movingo period ticket launched on September 30, 2017.

The Movingo ticket facilitated unlimited travel on SJ's regional trains and local public transport within the counties of Stockholm, Sörmland, Västmanland, Uppsala, Örebro, and Östergötland.

[8] Mälartåg is operated using a contract model, with Mälardalstrafik responsible for setting fares and service levels in collaboration with its six owner regions, as well as procuring rolling stock.

During this period, SJ operated trains using its existing fleet, which included locomotive-hauled passenger coaches and electric multiple units.

[20] Mälartåg's fleet primarily consists of Stadler DOSTO four-car double-deck electric multiple units, designated as ER1.

Features include inter-vehicle gangways with insulated twin bellows, large snowploughs, and underframes are designed to minimise freezing.