Ordered in July 1992 under the Clyde Ready Power contract along with the 82 class, the first batch of 31 locomotives were built by Electro-Motive Division in London, Ontario, Canada in 1994.

The second batch of four locomotives were delivered in November 2005, assembled by EDi Rail at Cardiff Workshops to the same specification from components imported from Canada and frames built in Port Augusta, South Australia.

The locomotives were designed with many component commonalities with the 82 Class for ease of maintenance at the Clyde Engineering Kooragang Island servicing facility, a purpose built maintenance depot for the 90 and 82 class locomotives constructed as part of the Clyde ReadyPower contract, opening in June 1994.

[2] With ARTC's intention for all Hunter Valley coal trains to operate using Electronically controlled pneumatic brakes (ECP) in the near future, a technology the 90 class do not possess.

What will happen is unclear as Pacific National have made conflicting statements and actions regarding whether the locomotives will be rebuilt or withdrawn from service in the near future, with members of the class coming in and out of storage, although none at this time have been scrapped.