Gary Dobson and David Norris have been found guilty of the murder of black teenager Stephen Lawrence in 1993.
Dobson, 36, and Norris, 35, were convicted by a unanimous jury at the Old Bailey and will be sentenced on Wednesday. Both had denied their involvement in the killing.
Speaking after the verdict, Doreen Lawrence, the mother of the victim, said: "Today is not a day to celebrate," adding: "How can I celebrate when my son lies buried."
It has been reported that both Dobson and Norris will be sentenced as juveniles, as they were 17 and 16 at the time of the killing.
There was total silence in court as the foreman of the jury said "guilty" when asked if the four women and eight men had reached verdicts on the murder charge.
There were tears from Lawrence's parents Neville and Doreen Lawrence in the public gallery as the verdict was announced, ending their 18-year search for justice.
Mr and Mrs Lawrence sat separately at the back of the court but both kept their composure and appeared to show little emotion.
But they slowly both began to weep as the results sunk in. Mr Lawrence covered his eyes and Mrs Lawrence was handed a handkerchief.
Speaking outside the court after the verdict, Doreen Lawrence said: "I would like to thank the jury for their verdict today. However today is not a cause for celebration.
"I cannot see him or speak to him or see him go to university or get married or have children. ... This verdict will not bring my son back."
In pointed criticism of the police, who failed to catch her son's killers in previous investigations, Mrs Lawrence added: "How can I celebrate when I know this day could have come 18 years ago?"
"Had the police done their job properly, I would have spent the last 18 years grieving for my son rather than fighting to get his killers to court."
Following the verdict, Cressida Dick, acting Metropolitan Police deputy commissioner, said it was a "huge regret to the Met that it has taken 18 years to get to this point".
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Dobson and Norris, both dressed in grey suits, stood with their hands behind them.
The judge, Justice Treacy, then asked for them to be taken down to the cells.
As he was leaving Dobson called out to the jury: "You have condemned an innocent man here. I hope you can live with yourselves."
His mother Pauline called out from the public gallery above: "He didn't kill that man."
Stephen Lawrence was killed in a racist attack by a gang of youths in Eltham, south east London in April 1993.
Duwayne Brooks, who was with Lawrence as he was attacked, tweeted his reaction:
The Stephen Lawrence Charitable Trust described its "sense of huge relief" as it welcomed the guilty verdicts.
Peter Bottomley, who was the Tory MP for Eltham at the time where Lawrence was murdered, said on the BBC: "Few can say that the colour of our skin is more important than the colour of our eyes."
Clive Efford, current Labour MP for Eltham, said he hoped the police investigation would continue if officers believe there were others involved.
Gary Dobson, and David Norris were arrested with Luke Knight, Neil Acourt and Jamie Acourt, in connection with his murder in May to June 1993, but the first investigation into Lawrence's death in April 1993 was lambasted after a public inquiry.
Dobson was acquitted of Lawrence's murder in 1996 after a private prosecution against him, Neil Acourt and Luke Knight failed.
Sir William Macpherson's 1999 report of the inquiry's findings called the standard of command in the vital first few hours after Mr Lawrence's killing "abysmal".
He branded the Met Police institutionally racist, and there were allegations by lawyers representing Mr Lawrence's parents that some officers were influenced by the former drugs baron father of David Norris.
Newspapers including the Daily Mail had campaigned for years to see Lawrence's killers brought to justice, going so far as to print the pictures of five men including Norris and Dobson under the headline "Murderers".
As soon as the verdict was announced the Mail published a story proclaiming it "the Mail's victory" including a video of editor Paul Dacre describing it as a "glorious" day.
Bevan Powell, chairman of the Metropolitan Black Police Association, said the verdicts "bring a sense of justice to a long overdue prosecution".
He added: "The Lawrences' persistence brought about a social consciousness which questioned and challenged the then existing inadequacies and failures inherent within the police and wider justice system to deliver fairness in cases which involved race and minority communities."
Acting Deputy Commissioner Cressida Dick paid tribute to Stephen Lawrence's family for contributing "to major changes within policing, the law and society as a whole" as she welcomed today's guilty verdicts.
Dick said: "It's a matter of huge regret to the Met that it has taken 18 years to get to this point."
She went on: "Every homicide case is incredibly important and we seek to bring the killers to justice. This case, which as you know has taken 18 years to get to this stage, is a unique case, not just for the Met but I think in modern policing.
Dick added that the verdicts were "not the end of the road" in the Lawrence investigation.Eyewitnesses to the fatal attack in 1993 said there were more than two assailants - five or six people engulfed the 18-year-old in a flurry of racist violence.
"if we get new evidence, if we have further opportunities, we will respond to that," Dick said.
She added: "And no doubt in the future the case will be reviewed, as other murders are if they are unresolved, to some extent.
"We don't see this as the end of the road."
The trial, which began at the Old Bailey on 14 November, concluded after seven weeks.
The historic court was opened especially during the holiday period so that the case could continue between Christmas and New Year.
Earlier, Justice Treacy had told the panel of four women and eight men that they must "reach verdicts on the basis of cool, calm consideration".
Success in cold cases including the death of Damilola Taylor sparked a new review which uncovered key forensic evidence in the Lawrence investigation.
A team of scientists at a private company called LGC were asked to "start again from scratch" in working to uncover evidence against whoever killed Mr Lawrence.
They carried out months of painstaking research before DS Alan Taylor and forensic scientist Rosalyn Hammond undertook the mammoth task of making sure forensic evidence had not arisen through contamination.
Gary Pugh, Director of Forensic Services for the Metropolitan Police, said: "The Damilola Taylor case...involved what LGC have done in going right back to basics and starting from scratch. Many of these cases have had reviews over time but quite often they're with a presumption that if nothing's been found the items aren't re-examined.
"What I think we've done here and in previous cases is start again from scratch and that was the brief we gave LGC in this particular case."
Edward Jarman from LGC said the firm was no longer examining items related to the case. The Met has no live lines of inquiry.
One of the convicted men, David Norris, had previously been linked to two other stabbings, one where he was acquitted and the other where the charges were dropped.
The month before Mr Lawrence died, Norris was accused of stabbing Stacey Benefield in the chest in Eltham High Street.
Benefield survived the attack and claimed he was offered £2,000 by someone believed to be Clifford Norris to withdraw support for the charges against his son. David Norris was later acquitted by a jury.
He had previously been accused of another knife attack on Darren Witham in 1992, but the charges were dropped the following year.
More recently, Norris and his friend Neil Acourt were jailed for 18 months in 2002 over a racist attack on an off-duty black police officer.