The British star, 41, is said to have helped a food delivery rider after he spotted him being beaten up by a gang of four people in central London.
Cumberbatch, who plays the crime-fighting supersleuth in the hit TV drama, was in an taxi on Marylebone High Street with his wife Sophie Hunter when they saw the victim hit over the head with a bottle.
He then reportedly ran towards them shouting to the attackers “leave him alone” and his quick-thinking actions are believed to have stopped the cyclist from suffering serious injuries.
It was claimed the celebrity managed to drag the gang off the victim before they tried to punch Benedict, but he fended them off and they fled.
The assault is said to have happened near Baker Street – the road where the fictional detective Sherlock Holmes lives.
According to The Sun, the TV and film star, who also stars in new Sky Atlantic TV drama Patrick Melrose, said: “I did it out of, well, I had to, you know.”
The driver of the car, Manuel Dias, told the newspaper: “Benedict was courageous, brave and selfless.
“If he hadn’t stepped in, the cyclist could have been seriously injured.”
He added: “Here was Sherlock Holmes fighting off four attackers just round the corner from Baker Street.
“He stood there instructing them in the street, shouting, ‘Leave him alone’.
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“I had hold of one lad and Benedict another. He seemed to know exactly what he was doing. He was very brave.
“He did most of it, to be honest.”