Steve Hart was born in Wangaratta on 13th Feb 1859** , his family had a 230 acre selection on Three Mile Creek. Not a great deal is known about Steve, however it is known that he entered towns in disguise as a female in order to scout banks. He was able to get by with this due to his slight and youthful appearance.
The police thought that dressed in such a fashion he was actually Ned’s sister Kate, hence Kate received credit for the actions of Steve on occasion. 

            In 1877 Steve was sentenced in to a years’ gaol for illegally using horses. He entered Beechworth gaol 
on 30 July 1877 and was released on 7 June 1878. Steve lived close to the race track and was know as a great rider-jockey. 
Max Brown said that Steve was the only person to manage the feat of jumping a horse over the Wangaratta railway gates.

“Steve Hart was born at Wangaratta in the year 1860, and, after leaving school at early age, worked on his parents’ 
farm on the Three-mile Creek. He became an expert bushman and an accomplished horseman. He fell in with the suggestion to join the Kelly youths when they were seeking alluvial gold on the Stringybark and Kelly’s Creeks. 
He, too, had experienced a period of police persecution, and doubtless found in the Kellys friends in need. 
He appears to have been possessed of considerable courage and resource, and during the period of his outlawry frequently rode about in feminine attire. So successful was this disguise that he was taken to be one of the Kelly sisters, and the police attributed many of his daring exploits to Kate Kelly. Steve Hart was never prominent as the Kelly brothers were, but he was at all times a faithful follower and courageous ally”.

Source: J.J. Kenneally.’The Inner History of the Kelly Gang’ 1969 edit.

Steve went to the Wangaratta Roman Catholic School, till about fifteen years of age, and then got with T.Obrien, Bill Monaghan, and the Clancy’s, all of whom were horse-dealing. The first time he got into trouble he was arrested by Sergeant Steele for stealing horses from David Green of Winton, but was convicted of illegally using, and sentenced
to four months’ imprisonment. After this he received similar sentences on two other charges—-in all, twelve months, which he served in Beechworth Gaol. He met Dan Kelly there, he having been convicted of riotous assault and indecent conduct at Winton, it was at this time that both lads laid the foundation of their friendship , which lasted til death. When Steve came out of gaol, Sergeant Steele advised him to be housed, and got his promise that he would. He commenced to work with his brother at fencing, but one day he took a sudden break, and giving a few blows with the axe, threw it down, swearing he would have a short life and a merry one, saddled his chestnut mare, and told his brother he would go shearing in New South Wales.

The Albury Banner & Wodonga Express July 17, 1880.