It is responsible for environmental protection, food production and standards, agriculture, fisheries and rural communities in the entire United Kingdom.

Defra also leads for the United Kingdom on agricultural, fisheries and environmental matters in international negotiations on sustainable development and climate change, although a new Department of Energy and Climate Change was created on 3 October 2008 to take over the last responsibility; later transferred to the Department for Business, Energy and Industrial Strategy following Theresa May's appointment as Prime Minister in July 2016.

Defra provides grant aid to the following flood and coastal erosion risk management operating authorities: Defra's overarching aim is sustainable development, which is defined as "development which enables all people throughout the world to satisfy their basic needs and enjoy a better quality of life without compromising the quality of life of future generations".

The Secretary of State wrote in a letter to the Prime Minister that he saw Defra's mission as enabling a move toward what the World Wide Fund for Nature (WWF) has called "one planet living".

[21] Under this overarching aim, Defra has five strategic priorities:[22] Defra aims to procure a significant proportion of the goods and services it requires from small and medium-sized enterprises (SMEs) in line with government policy on the SME agenda, and has also encouraged its major contractors to engage with SMEs.