Tammuz Brown was sentenced at the Old Bailey to life imprisonment for the murder of Malcolm Mide-Madariola with a knife outside Clapham South tube station in 2018.
Treynae Campbell, who provided Mr Brown with the knife, had previously admitted to possession of a knife and had been sentenced to 28 months at a Young Offenders Institute at an earlier hearing.
Zoe Johnson QC led Jocelyn Ledward for the prosecution.
This matter has received considerable press coverage; please see the BBC, the Evening Standard and the Metro.