Alan Blacker, known as Lord Harley in a trial last year, is said to have used titles which were "inaccurate".
He also appeared with St John Ambulance medals and ribbons on his chest, despite not being a St John member.
The Solicitors Disciplinary Tribunal is investigating.
Mr Blacker was defending minibus driver Andrzej Wojcicki, jailed for five years after being found guilty of causing the death of a cyclist by dangerous driving in Caerphilly county, when he was scolded by Judge David Wynn Morgan for his appearance.
He told him: "If you want to look like something out of Harry Potter you can forget coming to this court ever again."
Mr Blacker complained to the Judicial Conduct Investigations Office about the comments, saying he was upset his "qualifications, status and offices were brought into disrepute".
St John in Wales later said Mr Blacker was not a member of the Order of St John and it had contacted the police over the issue.
Now, the Solicitors Disciplinary Tribunal is looking into seven allegations, including that Mr Blacker:
The allegations are subject to a hearing before the Solicitors Disciplinary Tribunal and are as yet unproven.
A lawyer criticised by a judge for dressing "like something out of Harry Potter" is being investigated for allegedly misleading Cardiff Crown Court.