Matilda Simon, 3rd Baroness Simon of Wythenshawe CEng MIMechE (born 1955) is a British peeress, retired academic, woodworker, and Green Party member. In 2002 she succeeded her father as the Baron Simon of Wythenshawe. In 2015 she came out as a transgender woman. Her claim to the barony, following her gender transition, was accepted by the Lord Chancellor in 2022, so she became the first transgender peer of the realm.

Lady Simon was born in 1955, the second child of The Honourable Roger Simon and Anthea Daphne Simon.^[1] She was assigned male at birth.^[2] Her father was a solicitor, political activist, and left-wing journalist who served as secretary of the Labour Research Department. In 1960, her father inherited the Simon barony of Wythenshawe upon the death of his father, Ernest Simon, 1st Baron Simon of Wythenshawe, who was elevated to the peerage in 1947 by George VI.^[2] Her grandmother, Shena Simon, Lady Simon of Wythenshawe, was a feminist educationalist and politician and the eponym of the Shena Simon Campus of The Manchester College. Matilda Simon's great-grandfather was the Prussian engineer Henry Gustav Simon.

She was educated at St Paul's School, London, and graduated from the University of Oxford's Balliol College with a Bachelor of Arts degree.^[3] In 1983, she earned a Doctor of Philosophy from the University of Manchester.^[3][2]

From 1983 to 2013 she worked as a senior lecturer at Manchester Polytechnic and Sheffeld Hallam University.^[3] She was registered as a chartered engineer and as a member of the Institution of Mechanical Engineers in 1991.^[3] She is now a woodworker and furniture maker.^[4]

In March 2014, she and her partner founded Rollins Wood, a 7-acre community woodland in Marple Bridge, planting 1,200 trees the following year.^[5]

As Lady Simon was assigned male at birth, later coming out as a transgender woman in 2015, she inherited the Simon barony of Wythenshawe in 2002 after the death of her father, which only passes to the heirs male of the body of the first Baron. Her claim to the peerage was approved by the Lord Chancellor, Dominic Raab, in 2022 after she had changed her gender identity.^[6] According to the Gender Recognition Act 2004, a person changing gender does not affect the descent of any peerage or dignity or title of honour.^[7] In 2022, she successfully applied to be added to the "Register of Hereditary Peers", the list of "eligible hereditary peers who have indicated their wish to stand in by-elections for the House".^[6] However, she was removed from that list around May 2023.^[8]

The Daily Telegraph suggested she could stand in the by-election for the House of Lords in 2023 to replace Lucius Cary, 15th Viscount Falkland,^[2] but she did not do so. (Cary had been elected to the House as a Liberal Democrat in 1999, but switched to Crossbencher in 2011. By convention, he would be replaced by a Liberal Democrat, but peers from any party were allowed to stand for the by-election.) Had she succeeded Lord Falkland, she would have been the first transgender woman to join the House of Lords as one of the ninety-two hereditary peers.^[9] She would have become the first woman with a hereditary peerage to sit in the House of Lords since the retirement of Margaret of Mar, 31st Countess of Mar and the second transgender person in Parliament, after Jamie Wallis.^[10]

Most British peerages (including the Simon barony) can only be inherited by men under the system of agnatic primogeniture. No female hereditary peers have entered the House of Lords through the by-election process yet,^[6] since no woman has ever stood as a candidate for a by-election.^[11] Conservative politician Anne Jenkin, Baroness Jenkin of Kennington, and Charlotte Carew Pole, the daughter-in-law of Sir Richard Carew Pole, 13th Baronet, both called into question the validity of Lady Simon's peerage,^[2] since she is only able to hold the peerage due to being assigned male at birth.^[12] Carew Pole discussed Lady Simon's situation with The Daily Telegraph, saying, "Lady Matilda, Baron of Wythenshawe, has helped highlight several issues around inheritance and gender laws, where we now find ourselves in the absurd position of a younger son inheriting a title but identifying as a woman to stand in the hereditary peers by-elections, so keeping her new identity of a woman and the rights of a man to inherit."^[2] Carew Pole went on to question challenge the validity of Lady Simon's title, as she is not the eldest child of the 2nd Baron Simon of Wythenshawe and therefore, as she is also a woman, the title should go to her elder sister, The Hon. Margaret Simon.^[2] However, Margaret Simon could not have succeeded to the barony even if Matilda had been born female, as the barony can only be inherited by "heirs male of the body";^[12] it would have passed to a male-line cousin of Margaret and Matilda instead.