Chair of the Magistrates’ Association John Bache said it was “completely erroneous” that those with an old, minor criminal record would not be considered as candidates.
“We all make mistakes, we all do things we shouldn’t have done,” he told The Daily Telegraph.
“But we want to increase diversity, and if we did say anyone who’s ever done anything wrong ever isn’t going to be appointed that’s no way at all to increase diversity.”
There are just 16,000 magistrates in England and Wales – less than half the number 20 years ago, Mr Bache has previously said.
The role sees volunteers hear cases in criminal and family courts on issues like minor assaults, motoring offences and arranging for children to be taken into care.
Currently 12% of magistrates are from black or minority backgrounds, while only 4% are under 40, compared to 55% aged over 60.
Mr Bache said: “I wouldn’t want [candidates] to think that because they’ve got a relatively minor criminal record some years ago that they’re not going to be accepted as a magistrate, because that would be completely erroneous.
“People aren’t applying from ethnic minorities because they have the idea that people from their backgrounds don’t become magistrates and that is obviously erroneous.”
Magistrate candidates are expected to be “mature, understand people and have a sense of fairness”, according to guidance on the government’s website.
It also states those who had been found guilty of a serious crime or guilty of a number of minor offences would be unlikely to be considered for a post.