Margaret Thatcher became the first female Leader of the Conservative Party and Leader of the Opposition after winning the 1975 leadership election, the first Conservative leadership election where the post was not vacant. A rule change to enable the election was largely prompted by dissatisfaction with the incumbent leader, Edward Heath, who had lost three of four general elections as leader, including two in 1974. After announcing her first Shadow Cabinet in February 1975, she reshuffled it twice: in January and November 1976. Minor subsequent changes were necessary to respond to various circumstances. Thatcher's Shadow Cabinet ceased to exist upon her becoming Prime Minister following the 1979 general election.
Thatcher announced her first Shadow Cabinet on 18 February 1975.
On 15 January 1976, Thatcher reshuffled the Shadow Cabinet. Pym returned as Shadow Agriculture Minister, displacing Jopling. George Younger was dropped from the front bench, and he was replaced by Gilmour at Defence; Whitelaw, the Deputy Leader, added Gilmour's Home Affairs portfolio to his Devolution. John Biffen replaced Jenkin as Shadow Energy Secretary, and Jenkin took Health from Fowler, who was demoted to be a Shadow Transport Minister (which was not in Shadow Cabinet and was part of the Environment team).
On 19 November 1976, Thatcher reshuffled again. Maudling was dropped as Shadow Foreign Secretary and replaced by John Davies. Raison dropped, being replaced at Environment by Heseltine, who was replaced at the Industry portfolio by Biffen. He was in turn replaced as Shadow Energy Secretary by Tom King. Peyton and Pym switch roles (Shadow Leader of the House for Agriculture), with Pym also taking Devolution from Whitelaw.