King started his career at Swansea City but failed to make a first team appearance before joining Didcot Town.
The 31-year-old arrived at League One Scunthorpe from Preston in May 2015 and made 42 appearances for the Iron last season scoring two goals.
King is in contention for a place in the Stevenage side for their EFL Trophy fixture at Leyton Orient on Tuesday.
Scunthorpe United midfielder Jack King has joined League Two side Stevenage on loan until January 2017.