Neil Bright, 34, absconded from HMP Sudbury on Wednesday, February 17.
Bright was sentenced to life in prison at Stafford Crown Court in December 2018, for a section 18 assault with intent to cause grievous bodily harm.
Derbyshire Police say he has links to the Rugeley area – and has urged anyone who sees Bright not to approach him but call 101.
A spokesman for the force said: "Neil Bright, who is 34, absconded from the prison on Wednesday, February 17.
"He was sentenced to life in prison at Stafford Crown Court in December 2018 for a section 18 assault with intent to cause grievous bodily harm.
"Bright, who has links to Rugeley in Staffordshire, is white, around 6ft 1ins tall, of medium build and has blue eyes and short blonde hair.
"He was wearing a high visibility jacket when he left the prison at around 5pm walking towards the A50.
"If you have seen him or know of his whereabouts, please do not approach him, instead, contact us immediately."
Anyone who sees Bright should call 101, quoting incident number 775 of February 17.
Alternatively, call Crimestoppers anonymously on 0800 555111.