The 71-year-old media mogul, who owned Express Newspapers and OK magazine, pleaded guilty at Willesden Magistrates Court to two offences under the 1991 Dangerous Dogs Act.
The court heard his German Shepherd named Summer was “dangerously out of control” on March 30 this year.
Two people, Carl Allen and Mark Webber, were injured in the incident which happened in mansion-lined The Bishops Avenue in East Finchley.
As well as a fine the court ordered that the dog must remain muzzled in public places.
Prosecutor Martin Edwards told how the two victims, who were working in the area, suffered puncture wounds as a result of the attacks.
He read a statement to the court from Mr Allen which said: “The dog chased me and I called the police. It has bitten me through my work trousers.”
He said he had been left concerned about visiting addresses for work in case a dog attached him again.”
A statement from Mr Webber, a tree surgeon, said: “The dog lunged at me I got a puncture wound to my leg.”
The court heard that the pair had been going about their business when the canine attacked out of the blue.
In mitigation Mr Desmond’s defence counsel Philip Evans KC said the dog had been “startled” before the attacks possibly by the noise of a sliding van door and his client had accepted “full responsibility” over his dog’s actions.
He added: “He (Mr Desmond) is a man of thoroughly good character, there have been no other incidents involving Summer. There is considerable evidence he has taken this seriously.”
The court had heard the victims had raised the alarm after the out of control dog went for them.
Mr Allen in his evidence said he asked the media mogul: “Can you keep your dog under control he bit me.”
Mr Allen claims that in response the media mogul replied: “No he didn’t.”
Magistrate Mark Jabbitt addressing Mr Desmond said: “I accept you are a prominent businessman and philanthropist but you are responsible for your dog. There was a lapse in judgement. You have exercised responsible ownership since then.”
He added: “It does merit a fine. For each of the offences there will be a fine of £5000.”
Before the fine was issued Mr Desmond’s defence admitted he was “a man of some means.”
The judge also ordered the dog to wear a muzzle in public places. He warned that if Desmond did not follow that order and his dog reoffended it’s future would be “in peril” indicating it could be “destroyed.”
Mr Desmond was also ordered to pay £1,000 in compensation to each victim. In addition he is required to pay a £2,000 victim surcharge and £85 costs.