A British republican,[2] vegetarian, socialist[3] and self-described "radical lawyer",[4] he has participated in prominent and controversial court cases and inquests including the Birmingham Six, Bloody Sunday massacre, the Hillsborough disaster and the deaths of Jean Charles de Menezes and Princess Diana[5] and the McLibel case.

[6] As well as representing those wrongly convicted of the IRA's Guildford and Birmingham pub bombings, Mansfield has represented: the Angry Brigade; Dolours and Marian Price; Brian Keenan; the Orgreave miners; Mahmood Hussein Mattan, Ruth Ellis and James Hanratty (in posthumous appeals); those involved in the Israeli Embassy bombing; Frank Crichlow, owner of the Mangrove restaurant; Stephen Lawrence's family; Michael Barrymore at the Stuart Lubbock inquest; Barry George both at the inquest into the death of Jill Dando and George's wrongful conviction; the gangster Kenneth Noye;[7][8] the Bloody Sunday families; Arthur Scargill; Angela Cannings;[9] Fatmir Limaj, a Kosovo-Albanian leader prosecuted in the Hague; Mohamed al-Fayed in the inquest into the deaths of his son Dodi al-Fayed and Diana, Princess of Wales; the families of Jean Charles de Menezes and Mark Duggan; the Tottenham Three and the Cardiff Five.

And the moment a forensic scientist or anyone else says: 'I am sure this marries up with that' I get worried.In November 2019, along with other public figures, Mansfield signed a letter supporting Labour Party leader Jeremy 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 Corbyn in the 2019 UK general election.

[13] In December 2019, along with 42 other leading cultural figures, he signed a letter endorsing the Labour Party under Jeremy Corbyn's leadership in the 2019 general election.

The letter stated that "Labour's election manifesto under 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.