In October 2016 four bids were shortlisted for the next Wales & Borders franchise: Abellio, the incumbent operator Arriva, a Keolis/Amey joint venture, and MTR Corporation.

[9][10] In October 2017, Arriva withdrew from the bidding process, followed in February 2018 by Abellio, after the collapse of its partner Carillion.

[17] With a collapse in revenues, and a significant reduction in passenger numbers as a result of the COVID-19 pandemic having made the original franchise financially unviable, on 7 February 2021 the franchise was taken over by the Welsh Government's operator of last resort, Transport for Wales Rail, a subsidiary of Transport for Wales, with Amey Infrastructure having an involvement in delivering some key projects such as the Core Valley Lines.

[26][27][28] In April 2019, KeolisAmey Wales added five 153 units acquired from Great Western Railway to the eight it previously had.

[33] In September 2019, KeolisAmey Wales took delivery of the first of 12 Class 170 Turbostar DMUs from Abellio Greater Anglia.

Due to space limitations, Chrysalis Rail allowed KeolisAmey Wales to store any unallocated units or carriages at its Landore TMD in Swansea, even if they were not being worked on.

[39] From June 2019 to March 2020, KeolisAmey Wales hired two Class 37-hauled Mark 2 sets to temporarily operate rush-hour services between Cardiff and Rhymney to add capacity.

From January 2020 they were operating under PRM non-compliance dispensation, but were withdrawn in March due to decreasing reliability and replaced with trains formed of multiple Class 153 railcars coupled together, with many more of those in the fleet.