[3] Thornton was appointed to the High Court of England and Wales in February 2019, assigned to the Queen's Bench Division.

[1][6] Her mother was born in Wales, and her orthopaedic surgeon grandfather, who was based in Ammanford, was a speaker on social affairs.

[10] In 1988, she appeared as "Chrissie" in an episode of the long-running children's programme Dramarama titled "Snap Decision", which was aired in January 1989.

[13] She was appointed an Advisor to the British Government on Biotechnology and the Environment under New Labour in 2000, a role she held until 2005 and was later on the Attorney-General's C Panel.

She has also acted on behalf of the Welsh Assembly, and in 2009 was shortlisted for Chambers and Partners "Environmental and Planning Junior of the Year".

[14] Thornton was appointed Queen's Counsel (QC) in January 2016,[15][16][17] and a Deputy High Court Judge in May 2017.