Citytv stations originally had an intensely-local format based on newscasts aimed at younger viewers, nightly movies, and music and cultural programming. Moses Znaimer, who developed the original format, once described the system's philosophy by saying, "It's not the show, it's the flow".

The original Citytv station, granted callsign CITY-TV by the Canadian Radio-television and Telecommunications Commission (CRTC), was founded in Toronto in 1972 and began broadcasting for the first time on September 28 under the ownership of Channel Seventy-Nine Ltd; CHUM Limited acquired the station in 1981. Broadcasting on UHF channel 79 through its first decade, the station moved to channel 57 in 1983, where it remains to this day. In 1987, the station moved its headquarters from 99 Queen Street East to 299 Queen Street West (then known as the CHUM-City Building); one of the most recognizable landmarks in the city. On September 8, 2009, Citytv moved to its current location at Yonge-Dundas Square on 33 Dundas Street East.

Citytv gained a second station in Vancouver when CHUM bought CKVU from Canwest Global in 2001. The station became Citytv Vancouver on July 22, 2002. Prior to CHUM's acquisition of CKVU, some Citytv programming was syndicated to KVOS in nearby Bellingham, Washington.

In 2004, CHUM bought Craig Media Inc., parent of the A-Channel system in Manitoba and Alberta. The Craig-owned A-Channel stations were relaunched as Citytv on August 2, 2005; the same date when CHUM's NewNet stations were rebranded under the A-Channel banner.

On July 12, 2006, Citytv parent CHUM Limited announced plans to sell its broadcasting assets to CTV parent CTVglobemedia. CTVgm initially intended to retain CHUM's Citytv system while divesting CHUM's A-Channel stations and Access Alberta in order for the CRTC to approve the acquisition.

On the same day that the takeover was announced, Citytv canceled its supper hour, late night, and weekend newscasts at its local Vancouver, Edmonton, Calgary and Winnipeg stations, laying off hundreds of news department staff.

In October 2006, Citytv launched a daily national newscast, CityNews International. It is produced in Toronto for broadcast on the western Canadian stations, as well as on CHUM's Toronto news channel CP24. The Edmonton and Calgary stations also began broadcasting a daily 30-minute magazine show, Your City, instead of a full-fledged newscast. The Vancouver news operation, which had operated for 30 years under various owners and station identities, was not maintained aside from BT.

In the same month, Citytv Toronto began broadcasting local news in high-definition, becoming the first television station in Canada to do so.

On June 8, 2007, the CRTC approved the CTV takeover of CHUM. However, the CRTC made the deal conditional on CTV divesting itself of Citytv. On June 11, 2007, CTV announed that it would retain the A-Channel stations, and sell the Citytv stations to Rogers Communications for $375 million. The transaction was approved by the CRTC on September 28 and was completed on October 31, 2007.

Citytv is well known for its unconventional approach to news and local programming. There is no news desk (anchors read the news standing up, or on stools), and cameras are sometimes hand-held. Citytv also pioneered the concept of videojournalism, where reporters often carry their own cameras and report and videotape their own stories. Citytv calls its videojournalists "videographers", but unlike many American television markets that try to conceal the fact that reporters are so-called "one-man bands", Citytv embraced the use of video journalism by highlighting the use of technology; Citytv videographers often carry a second home video camera to record images of them videotaping on the scene. The low-grade video is then incorporated into the final story to show viewers how the story was recorded.