The company was founded in 1945 as York Broadcasters Limited when it launched CHUM-AM 1050 but was acquired by salesman Allan Waters in 1954.

In July 2006, one year after the death of Waters, CHUM agreed to merge with CTVglobemedia (now Bell Media), owner of the CTV Television Network.

The merger was completed on June 22, 2007; regulatory approval was made conditional on the sale of CHUM's five Citytv stations to Rogers Communications.

CHUM Limited began operations when CHUM-AM was founded in 1945 by four Toronto businessmen, including Al Leary, a former sportscaster, who had been the station manager at CKCL for 14 years.

The station, then operating from studios in the Mutual Street Arena, broadcast a format typical of the late 1940s, with a combination of information, music, and sports.

When CHUM was about to debut, Leary told the press that the new station would be known for community service and in-depth news, in addition to live talent and the most popular phonograph records.

CITY-TV – the Toronto UHF station launched with great flair and style in 1972 by Moses Znaimer – ran into financial debt by 1975.

Multiple Access Ltd. (the owners of CFCF in Montreal) purchased 45% of the station in 1977, and sold its stake to CHUM Limited three years later.

The experiment was successful enough that CHUM replicated CKVR's format on several stations it had acquired from Baton Broadcasting in 1997, including CHRO in Pembroke, CFPL in London, CKNX in Wingham, and CHWI in Windsor.

Prior to CHUM's acquisition of CKVU, some Citytv programming was syndicated to KVOS in nearby Bellingham, Washington.

Moses Znaimer retired from active management at CHUM in April 2003, and briefly continued to work on projects with the company, before moving on to other ventures such as ZoomerMedia.

On December 1, 2004, CHUM purchased Craig Media Inc., which owned five local TV stations, mainly in the Prairies, and three digital specialty services, for $265 million CAD.

CHUM announced in February 2005 that the NewNet stations would be relaunched under the A-Channel brand by that fall; the rebrand took place on August 2, 2005, the same date when the former A-Channel stations in Winnipeg, Edmonton and Calgary, recently acquired by CHUM from Craig Media, were relaunched under the Citytv brand.

[10] At the same time, CHUM announced plans to consolidate the master control departments for CKVR, CFPL, CHRO, CHWI and CKNX at 299 Queen Street West in Toronto, as well as the traffic and programming departments at CFPL, resulting in the loss of approximately nine staff members from CKVR.

Following tributes from across Canada, more than 2,000 attended a celebration of his life at Toronto's Westin Harbour Castle Conference Centre.

[12] CTVgm's takeover bid was completed on October 30, although CHUM was immediately in a blind trust under lawyer John McKellar.

CHUM claims the layoffs were part of an ongoing process to streamline its operations and not directly related to the takeover.

As Shaw Communications purchasing the Global Television Network and the Canwest television properties, Vidéotron launching its wireless telephone network with video content as a key selling point,[15] and the enormous popularity of wireless and Internet video and other media streams at the 2010 Vancouver Olympics,[16] Bell once again sought to bring a content provider into its portfolio.

[17][18] In November, 2004, CHUM and Astral Media filed an application with the Canadian Radio-television and Telecommunications Commission for a subscription radio service in Canada.