Theresa Villiers is to be replaced as secretary of state as Briitsh Prime Minister Theresa May continues to reshuffle her cabinet.
Ms Villiers said she was offered a role in the new government but "it was not one which I felt I could take on."
During the race for Tory leadership, Ms Villiers supported Theresa May's opponent Andrea Leadsom.
Ms Villiers' exit was met by contrasting reactions from the DUP and Sinn Fein.
DUP leader Mrs Foster tweeted: "I enjoyed working with her & wish her all the best for the future."
Sinn Fein MEP Martina Anderson struck a very different tone.
"Theresa Villiers will be no loss - all British Secretary of States should stay over there," she tweeted.