Ahmed Omar Saeed Sheikh has been sentenced to death for abducting and murdering the Wall Street Journal reporter.
Responding to the sentence a Foreign Office spokesman said the UK Government supported the verdicts, but opposed the death penalty.
"Although we support the suspected terrorists being brought to justice it is well known that we oppose the death penalty in all circumstances," he said.
"The Pakistani authorities are already well aware of our position on this issue."
In addition to the death sentence for Omar Sheikh, three fellow militants were given 25-year prison sentences.
London-born Omar Sheikh is to appeal his sentence, his defence said.
Excluded journalists
The trial was held in a heavily guarded jail in Hyderabad.
During sentencing reporters were excluded but were briefed afterwards by court officials.
The trial began on 22 April in Karachi, but was transferred to Hyderabad after prosecutors said they feared for their lives.
A body which police believe may be that of Mr Pearl was found in May, but the results of DNA tests have yet to be announced.
Omar Sheikh had described the evidence against him as "a tissue of lies" and said it had been fabricated "to please the Americans".
And he has accused the police of forcing his co-defendants to make statements implicating him.
His lawyer Abdul Waheed Katpar told the court last week that testimony by several prosecution witnesses was contradictory.
Doubt?
He also said that allegations that evidence was fabricated and confessions coerced had not been answered.
In such circumstances, the benefit of the doubt should go to the defendants, Mr Katpar argued.
The prosecution has alleged that Omar Sheikh was seen meeting Daniel Pearl at a restaurant in Karachi on the day he disappeared.
Defence lawyers deny he was in Karachi at the time.