Miliband, MP for South Shields since 2001, has held a number of government positions, including minister of communities and local government, minister for the Cabinet Office and minister of state for schools.
Miliband replaces Margaret Beckett, who has become foreign secretary.
Peter Kendall, president of the NFU, met Miliband this week, and said: "He was very open about his need to learn about the industry and I am looking forward to working with him and his team."
Also in the reshuffle, Lord Bach, sustainable food and farming minister, was at first replaced by Baroness Ashton. However, she has in turn now been replaced by Lord Rooker.