The Fairfield City Council is a local government area in the west of Sydney, in the state of New South Wales, Australia. The council was first incorporated as the "Municipal District of Smithfield and Fairfield" on 8 December 1888, and the council's name was changed to the "Municipality of Fairfield" in 1920, before being proclaimed a city in 1979. The City of Fairfield comprises an area of 102 square kilometres (39 sq mi) and as of the 2021 census had a population of 208,475. The mayor of the City of Fairfield is Cr. Frank Carbone, the first popularly-elected independent mayor of Fairfield.

Fairfield is considered one of the most ethnically diverse suburbs in Australia. At the 2021 census, the proportion of residents in the Fairfield local government area who stated their ancestry as Vietnamese and Assyrian, was in excess of sixteen times the national average. The area was linguistically diverse, with Vietnamese, Arabic, Assyrian Neo-Aramaic, or Cantonese languages spoken in households, and ranged from two times to seventeen times the national averages.

The Smithfield–Wetherill Park Industrial Estate is the largest industrial estate in the Southern Hemisphere and is the centre of manufacturing and distribution in Greater Western Sydney, with more than 1,000 manufacturing, wholesale, transport and service firms.

A few small areas of the original bushland remain, including examples of Cumberland Plain Woodland, which is listed under the Threatened Species Conservation Act, and the Cooks River/Castlereagh Ironbark ecological community. There are 580 parks (60 of which are major parks), including one of the largest urban parks in the world, Western Sydney Parklands, which has a precinct that lies in the Fairfield area, called the Western Sydney Regional Park.

Creeks flowing in the area include Prospect Creek, Cabramatta Creek, Clear Paddock Creek and Green Valley Creek. The creeks streamed through what the settlers described as "a chain of ponds" down to the Georges River, rather than an unbroken stream, before the disturbance of the banks by the European settlers. De Freitas Wetland was one of the many ponds of Prospect Creek. On a map today, the creeks resemble three fingers creeping out westward from the river.

Fairfield City is mainly residential in nature with large-scale industrial estates at Wetherill Park and Smithfield. Fairfield Showground is an important cultural venue. Prominent roads such as Cumberland Highway and The Horsley Drive wind through it. Wetherill Park is listed as one of the five most leafiest suburbs in Sydney by the Domain Group, being the only suburb in Western Sydney to be listed (since most leafy suburbs are within Northern Sydney).

Suburbs in the City of Fairfield are:

For more than 30,000 years, Aboriginal people from the Cabrogal–Gandangara tribe have lived in the area.