She was called to the bar by Inner Temple in 1987 and became a QC in 2006. Simler was appointed a Recorder in 2002 and was a judge of the High Court of Justice (Queen's Bench Division) from 2013. She was President of the Employment Appeal Tribunal for a term of three years from 1 January 2016 to 31 December 2018.[3]
On 27 June 2018, it was announced that Simler was to be appointed to the Court of Appeal (England and Wales), an appointment she took up on 2 July 2019.[4]
Simler was chair of the Equality and Diversity Committee of the Bar Council of England and Wales,[5] and at the date of announcement of her appointment to the High Court bench in 2013 she was head of her chambers.[6] She is the chair of the Equality, Diversity and Inclusion sub-committee of the Inner Temple.[7]
On 17 October 2023, the Ministry of Justice announced that Simler would become a Justice of the Supreme Court of the United Kingdom.[8] She was sworn in on 14 November 2023.[9]