In 1949, through a special Act of the Parliament of Canada, he incorporated Westcoast Transmission Co. Ltd. whose business plan included the construction of a 650-mile gas pipeline from Taylor in north-eastern British Columbia to the United States.

McMahon personally began lobbying the Canadian and American governments to remove their restrictions on the export and import of natural gas.

In 1964, Westcoast Transmission built another processing plant at Fort Nelson, British Columbia in support of an additional 250-mile line to the company's new discoveries in the Canadian Northwest.

In 1974, Westcoast Tramsmission created Foothills Pipeline Ltd., a subsidiary company established to build and operate the Canadian portions of the Alaska Natural Gas Transportation System.

[2] The natural gas pipeline business was later spun off as part of Spectra Energy, which merged with Enbridge in 2017.