Marques Walker previously admitted attacking Jermaine Cools in November 2021.
The 17-year-old, who was 16 at the time of the killing, has been sentenced to a minimum of 19 years behind bars.
He was also sentenced to a minimum of 4 years for a separate offence of GBH, which happened when he was on remand at HMP Feltham.
Jermaine Cools was London’s youngest stabbing victim in 2021.