Jeremy Corbyn assumed the position of Leader of the Opposition after being elected as leader of the Labour Party on 12 September 2015; the election was triggered by Ed Miliband's resignation following the Labour Party's electoral defeat at the 2015 general election when David Cameron formed a majority Conservative government. The usual number of junior shadow ministers were also appointed.

The 2015 Labour Party leadership election was triggered by the resignation of Ed Miliband as Leader of the Labour Party on 8 May 2015, following the party's defeat at the 2015 general election. Harriet Harman, the Deputy Leader, became Acting Leader but announced that she would stand down following the leadership election. It was won by Jeremy Corbyn in the first round. Coterminous with the leadership election, in the 2015 Labour Party deputy leadership election, Tom Watson was elected to succeed Harman as deputy leader.