They lived in a house in Russell Street on the Northside of Dublin which belonged to Christina, who owned a number of properties in the area.
There is no evidence that he entered the Society of Jesus (Jesuits), however there is an oral history which suggest he spent less than six months as a brother-novice at St Stanislaus College, Tullabeg, Rahan, County Offaly; according to surviving members of his family, Behan was found in a compromising situation involving one of the college's domestic servants.
According to Behan himself, he found this an attractive method of extricating himself from a path that had not been chosen by him.
Later he joined the Irish Republican Army and became one of Michael Collins' Twelve Apostles, responsible for assassinating British Army officers during the Anglo-Irish War.
Unusually for an author, he never recorded his service with the Bureau of Military History, and is not recorded in any of the other witnesses' statements, so his exact role must remain anecdotal, and not verifiable.During the Irish Civil War, Behan fought on the anti-treaty side and was incarcerated in both the Curragh Military Prison and Mountjoy Prison.
Prior to his imprisonment, Behan had completed a teaching qualification, but after the Irish Free State was created, all government workers (teachers included) were required to swear an oath of allegiance to the new state, and "fidelity" to its head of state, George V.
Behan's choice to refuse to take such an oath of loyalty resulted in self-exclusion from the teaching profession for which he had trained and ultimately a life of comparative hardship.
Behan became a painter and decorator, and married Kathleen Kearney in 1922.
Kathleen's brother Peadar Kearney was a famous songwriter and poet (famous for writing the Irish National Anthem 'A Soldier's Song', 'Down by the Glenside' and the 'Foggy Dew').
Whilst Behan was incarcerated, his first child (Brendan) was born.
Behan's first sight of Brendan was from a window in the prison that looked out to the streets below, as Kathleen held the child up for him to see.
According to his children, Behan was an extremely influential force; a talented teacher, he read from the classics to his children in the evenings before bedtime; he encouraged his wife Kathleen to take their children on literary tours of the city, thus were the seeds of creativity nurtured.
Stephen was the subject of This Is Your Life in December 1962 when he was surprised by Eamonn Andrews in the audience of Dublin’s RTÉ Studios.
The producers of the program had originally intended to cover the life of Brendan, Stephen's eldest son, however, as they researched Stephen's life, it became clear Stephen was a much more interesting subject; Behan was taken to the TV studios by Irish International Rugby player Tony O'Reilly a long time friend of Behan.