Garfield's appointment means she will be one of four female chief executives in the FTSE 100 (becoming three when Angela Ahrendts leaves Burberry for Apple next year). The other two are Carolyn McCall, EasyJet, and Alison Cooper, Imperial Tobacco.
Garfield, who spearheaded the roll-out of fibre broadband across Britain at BT Openreach, will take over from Severn Trent's outgoing CEO Tony Wray in Spring 2014.
She has been at BT since 2004 and CEO of Openreach since 2011. Previous to that, Garfield held several positions at BT, including group director of strategy and regulation, and managing director of commercial and brands and UK customer services director, within BT's Global Services division.
Garfield is currently a non-executive director at Tesco.
"It is a huge wrench to leave Openreach but I feel the time is now right to take on a fresh challenge," said Garfield. "Our commercial programme to bring fibre broadband to two-thirds of UK premises is almost complete, while BT's public sector broadband partnerships are making good progress."
Andrew Duff, chairman of Severn Trent, said: "We are delighted that Liv is joining us. She brings experience of managing customer service delivery and complex organisations in a regulated environment."
