In November 2019, along with other public figures, Martinez signed a letter supporting Corbyn, describing him as "a beacon of hope in the struggle against emergent far-right nationalism, xenophobia and racism in much of the democratic world" and endorsed him in the 2019 UK general election. In December 2019, along with 42 other leading cultural figures, she signed a letter endorsing the Labour Party under Corbyn's leadership in the 2019 general election. The letter stated that "Labour's election manifesto under Jeremy Corbyn's leadership offers a transformative plan that prioritises the needs of people and the planet over private profit and the vested interests of a few."