He was a "difficult child" according to writers Maurice Gurvich and Christopher Wray.
At 16 years of age, he ran away to sea, and thereafter he began a long career of crime, largely thieving and obtaining money under false pretenses.
He was also responsible for the murder of his first wife Marie and his four children at Rainhill, England, on or about 26 July 1891, and a second wife, Emily Mather, at Windsor, Melbourne, on 24 December 1891.
Less than three months elapsed between the discovery of Mather's body in Windsor, Melbourne, in March 1892, and Deeming's execution for her murder in May 1892; a remarkably short time by comparison to modern western legal standards.
This was not only due to efficient police work, but also a result of the considerable international media interest the murder attracted.
For example, it was an English journalist working for the Melbourne Argus who first approached Mather's mother in Rainhill and delivered the news of her daughter's murder.
Another factor was Deeming's behaviour in public, for while he often used different names, he usually drew attention to himself with behaviour variously described as aggressive, ostentatious, ingratiating and overly attentive to women.