Villiers served as secretary of state for Northern Ireland between 2012-2016 under David Cameron.
She has also served as transport minister from May 2010 until September 2012 and was elected Conservative MP for Chipping Barnet in 2005.
She joins Defra at a critical time and will oversee the implementation of the Environment Bill, which includes many waste and resources commitments including extended producer responsibility, a deposit return scheme for England and changes in household collection systems.
After graduating from university, Villiers worked as a barrister and a lecturer in law at Kings College, London.
She is a Brexiteer and has argued for a No Deal Brexit, which many fear would be damaging for UK green policy.
In a Facebook post, she said: “I feel very honoured to have been asked by the Prime Minister to return to the Cabinet, taking on the role of Secretary of State for the Department of the Environment, Food and Rural Affairs. I have championed a number of the issues covered by the department, including animal welfare and improving air quality.
“My new responsibilities will therefore complement many of my local campaigns in my constituency, such as protecting our green spaces. I am already hard at work preparing for Defra questions in Parliament tomorrow morning.”
Villiers is the sixth person to become environment secretary since 2010.