Thirty six year old Mark Pickering was inside the cathedral undertaking his duties when it happened on Monday afternoon.
At around 2pm, a man walked up and punched him in the face, before kicking and stamping on him while he was on the floor.
He then grabbed a church candle, hit him several times in the face and then fled the scene.
Mr Pickering was left with two broken ribs, a fractured elbow and head injuries after the attack.
He was taken to the Royal Blackburn Hospital by ambulance, where he needed surgery on his arm.
Dean of the Cathedral, the Very Revd Christopher Armstrong says everyone was shocked by the "unprovoked attack" on a member of their cathedral staff, adding:
"Mr Pickering was just making polite conversation when the attack happened.
"It is a huge shock to us all. This sort of level of attack happens very rarely, but it is the worst I have known for 14 years."
He went on: "Our vergers are very skilled at making people feel welcome.
"The cathedral is open during extended offices hours and this was a member of the public who made an unprovoked attack.
"Mr Pickering is very experienced. He is the Dean's verger and he is head of the department.
"He is the most placid and caring person you can imagine.
"He is one of the stars of the cathedral staff and he is widely acknowledged as a brilliant carer and reconciliator, not only by the cathedral staff, but also members of the public who deal with him."
A 24 year-old man's been arrested and reportedly sectioned, after assessment by a mental health team.