[6] He first set precedent in the UK when he secured first unlawful killing decision against a serving police officer in the Azelle Rodney public shooting enquiry in 2013.
In 2015, he was the counsel for the parents of Christianne and Robert Shepherd who died of carbon monoxide poisoning while on holiday in Corfu in October 2006.
The hearing centred around controversial decisions taken by former First Minister of Wales Carwyn Jones prior to Mr Sargeant's suicide.
Thomas successfully prevented Cathryn McGahey QC (representing Jones) from introducing unproven allegations of misconduct against Sargeant to the inquiry, insisting that the "deceased person is not here to defend themselves" and that "there has been no investigation into these rumours and suspicion".
In siding with Thomas, coroner, John Gittins, ruled that the effort by McGahey on behalf of Carwyn Jones was "astounding" and "opportunistic".