Englishman Brown becomes the third player to leave St Mirren in a matter of weeks following a court appearance.
Kevin van Veen’s loan spell was ended last week after the Dutch striker appeared in court charged with domestic abuse.
Last month, defender Shaun Rooney left St Mirren by mutual consent after being charged with assault following an incident in a Glasgow takeaway.
St Mirren have moved quickly to replace Brown by handing 29-year-old John, who has been capped seven times by Wales, a contract until January.
John had a previous spell in the Scottish Premiership with Rangers, having originally arrived on loan from Cardiff City before signing permanently in 2018.
He made 30 appearances over the course of a year before moving on to Swansea City then Bolton Wanderers.
John was released in June following a loan spell with Salford City.