John Georgelas, who uses the name Yahya Abu Hassan, quietly married Joya Choudhury, at the town hall in Rochdale, Lancashire, in north-west England after her family disapproved of the marriage and disowned her, the Sunday Times reported.
The couple met online while Choudhury, then 19, was at college.
Georgelas persuaded his British wife Choudhry to enter the warzone with their three young sons while she was pregnant with their fourth child.
Georgelas is now a key propagandist and recruiter for ISIS and his activities are believed to have led to him being placed on a US government "kill list".
The 33-year-old's conversion and rise within the ISIS ranks was reportedly fuelled in part by his time in Britain before he joined the terror group in Syria in 2013.