Son of the Rev. Alfred Barrett (and brother of Katherine Price Hughes), he trained as a doctor at Edinburgh. During practice in the 1870s in the East End of London, he was horrified by the effects of starvation, smallpox and cholera in the Docklands area. Opening a practice in the West End, he became involved in the work of the West London Mission. As Honorary Superintendent of its Medical Department, he was available for free consultation in his surgery every Friday morning.He was assisted by Henry Lunn and the Mission Sisters as visitors to people's homes.