Dino Donaldson attacked Anojan Gnaneswaran in January 2024 after a row broke out about between two groups of men over a drug deal.
21-year-old Donaldson was found guilty following a trial at the Old Bailey and will be sentenced at a later date.
The court heard how he pushed his victim onto the railway tracks and stabbed him in the chest, abdomen and thigh.
Gnaneswaran was pronounced dead at the scene.
