Monsarrat was born in Kendal. He was educated at King William's College on the Isle of Man. In 1890 he joined Edinburgh University as a medical student and graduated M.B., Ch.B. in 1894. He worked at Nottingham General Hospital and Great Yarmouth Hospital. He moved to Liverpool and obtained F.R.C.S. in 1897. He married the same year and took up medical practice in Liverpool.
