Harry was stabbed in the neck at a New Year's Eve fireworks event in North London.
Aries Lloyd-Hall, now 18, was convicted after a retrial at the Old Bailey in October, following a hung jury in the first trial.
The jury had previously heard that the fatal stabbing on Primrose Hill on December 31, 2023, occurred when Harry accidentally bumped into another boy while "play-fighting" and practicing high kicks.
Lloyd-Hall, from Westminster, was found guilty by a majority verdict of 11 to one after almost eight hours of deliberation. He had already been convicted of possessing an offensive weapon.
Sentencing him on Monday, in proceedings shown on television, Justice Cavanagh said Lloyd-Hall carried the knife to feel "powerful" and to show "bravado" – not for self-defence, as he had claimed at his trial.
He said Harry was a typical "mischievous and energetic" 16-year-old who was "very engaging".
The judge said: "You stabbed Harry because you were angry with him and you were trying to look big in front of your friends."
In that "split second," he must have realised Harry could be killed or seriously injured, but Justice Cavanagh said: "At that moment you didn't care whether he lived or died."
The judge added that the case clearly demonstrated the dangers of young people carrying knives in public places and should serve as a warning and a lesson.
Lloyd-Hall, who was 16 at the time, attacked Harry after he accidentally bumped into another boy. Both men, who had arrived separately, were part of the crowd gathered on Primrose Hill to watch the fireworks over the River Thames.
Lloyd-Hall attacked Harry with a pointed dagger, just metres from where uniformed police officers were stationed.
He collapsed and died within minutes, shortly before midnight.
Lloyd-Hall claimed he thought he had only struck Harry with the sheath in an to attempt to push him away.
Members of Harry’s family wept and hugged each other after Lloyd-Hall was led down from the dock. Harry’s older sister, Tella Lohan, told the court the family was struggling to come to terms with the “senseless and brutal” killing.
She said that on hearing he had been injured, his parents had rushed to the park to be with their son.
Reading a victim impact statement, she said: “As a family, we are all heartbroken that 2023 was the first year we didn’t celebrate together.
“Harry went to celebrate with his friends and he didn’t come home.”
Miss Lohan said the sound of fireworks at any time of year now brings back their grief, and that it “will never be a Happy New Year for our family again”.
She described her brother as intelligent, energetic and a natural entrepreneur, who had studied law at college and dreamed of a career in the Army like his great-grandfather.
She said he was a huge Tottenham Hotspur fan and also enjoyed boxing, and was very popular among his friends.