The 29 year old appeared at Blackfriars Crown Court in south London and pleaded guilty to robbery, attempted robbery, and possession of a firearm.
He and his co-defendant Terry Heywood were given indeterminate sentences to protect the public.
Henry was previously convicted of raping an Austrian tourist and leaving her to drown in a canal as part of a sickening gang attack when he was just 14.
The Bleeding Love hitmaker has previously spoken out about her family, revealing: "There are bad people in my family, but we didn't really mix with them... I saw the pain that someone else's badness caused for other people. You have to think and make your own mind up."