Sir Nicholas Mostyn was a barrister for 30 years specialising in major divorce cases, some involving celebrities such as Paul McCartney and Princess Diana, which earned him the reputation as "the scariest barrister in Britain". He became a High Court judge in 2010 and sat in the Family Division. He was also a judge of the Court of Protection and the Administrative Court of the King’s Bench Division of the High Court, where he heard many judicial reviews of government decisions. 

Renowned for his independent and outspoken style, he frequently challenged the received wisdom of the law in favour of justice.