The TV presenter, Garnier Nutrisse's first celebrity brand ambassador, will appear in a 拢7m campaign.
L'Oreal is hoping that the launch of the permanent colorant product will capture some of the thousands of women who currently use professional salons rather than colourants because of their mistrust of off-the-shelf products.
From November, McCall will appear in TV and press ads created by Publicis, where she talks on the phone to her mother about the difference the product has made.
The activity will be supported by a direct campaign including point-of-purchase, internet and customer relationship marketing.
Garnier Nutrisse is the 12th-biggest brand in the UK hair colourant market in terms of retail value, according to Euromonitor.