Shaw was founded as Capital Cable Television Company, Ltd. in Edmonton, Alberta, in 1966. The company changed its name to Shaw Cablesystems Ltd. and went public on the TSX in 1983. The company grew during the 1980s and 1990s through acquisitions of firms including Classicomm in the Toronto area, Access Communications in Nova Scotia, Fundy Cable in New Brunswick, Trillium Cable in Ontario, Telecable in Saskatchewan, Greater Winnipeg Cablevision (serving areas east of the Red River), and Videon Cablesystems of Winnipeg (serving areas west of the Red River), which had itself previously acquired Vidéotron's assets in Alberta. However, two swaps, in 1994 and 2001, with Rogers Cable have resulted in its assets being restricted to Western Canada and a few areas of Northern Ontario. In 1999, Shaw spun out its media properties into a second publicly-traded company, Corus Entertainment. In 2001 the Moffat family sold Videon Cablesystems to Shaw.
Prior to 2003, Shaw owned cable systems in the United States previously owned by Moffat Communications, serving six communities in Florida (Eastern Pasco County, Clermont, Palm Coast, Ormond Beach, West Palm Beach and Doral), and the Houston, Texas suburbs of Kingwood, Lake Conroe and Lake Livingston. In February 2003, the Florida systems would be sold to Time Warner Cable (with the West Palm Beach and Doral systems later sold to Comcast, and the other systems spun off to Bright House Networks), while the Texas systems were sold to Cequel III, as part of its then-Cebridge Connections subsidiary (now Suddenlink Communications).
In 2008, Shaw entered the AWS spectrum auction with the intention of possibly becoming a wireless phone provider. The auction ended July 2008, giving Shaw Communications enough spectrum to build a wireless network in its home provinces of British Columbia, Alberta, Saskatchewan, Manitoba and Ontario. This spectrum ultimately went unused and was sold to Rogers Communications in January 2013.
In July 2009, Shaw announced its acquisition of Mountain Cablevision; in September, Rogers sued Shaw to block the sale, citing violations of a non-compete clause. However, the suit was quickly dismissed by the Ontario Superior Court. The purchase was approved by the CRTC on October 22, 2009. The acquisition was Shaw's first cable property east of Sault Ste. Marie since the 2001 swaps with Rogers and Cogeco. Shaw's re-entry into Southern Ontario would be short-lived, as its Hamilton system would be resold to Rogers in January 2013 as part of a deal which also saw unused wireless spectrum sold to the company, and saw Rogers sell its stake in specialty channel TVtropolis.
On April 30, 2009, Shaw announced a deal to acquire three television stations — CHWI-TV in Windsor, Ontario, CKNX-TV in Wingham, Ontario and CKX-TV in Brandon, Manitoba — from CTVglobemedia. CTV had indicated that it would shut down the stations, all of which were incurring extensive financial losses, later in the year if a buyer could not be found, and had placed them on the market at a price of just $1 each. However, it was reported on June 30, 2009 that Shaw has backed out of the deal and is declining to complete the purchase. CHWI-TV would remain on the air as is; CKNX-TV would become a repeater of London station CFPL-TV in September 2009, while CKX-TV would close down entirely in October 2009.