Until 1917, new lines in NSW were constructed by the Public Works Department. For the purposes of route-building, the NSW PWD maintained a small, fleet of superseded locomotives. To replace their aging fleet, the PWD placed an order for eight 2-6-0 tender locomotives with Hunset Engine Co in Leeds. The class entered service numbered PWD 1-8 in February to May, 1913.

In January 1917, the NSWGR took over construction of new lines, and absorbed the former PWD locomotives into their fleet. The class were reclassified as the "G Class" and numbered 1204-1211. Given that the G Class were more modern than a lot of other locomotives in the NSWGR fleet, they were reallocated to Hunter Valley coal and Sydney freight workings.

An early issue with the G Class was their rigid frames, which caused issues when operating through tight curves. This lead to the class being transferred to Narrabri West for use on the branch lines in the north-west of the state. Later classified as the Z27 Class, they would continue to work the north-west of the state until displaced by 30T class, themselves displaced by dieselisation elsewhere in the state.

Once the 48 Class were introduced to the north-west of the state, the class were withdrawn altogether with the final operational member set aside for preservation (see below).