The footage shows the man strangle the 37-year-old victim, who was on his way to work and police say has been “highly traumatised” by the attack.
After the victim passed out briefly and regained consciousness, the attacker tried to strangle him again.
The assault took place on a single decker C1 bus in around 1.50pm on Saturday.
Met Police say the bus was going to White City when the attacker got on at Cresswell Gardens and sat down behind the victim.
The pair spoke briefly, before the man in front is choked.
The victim was helped by other passengers before reporting the incident to police.
The suspect is a black male believed to be in his early to mid 20s. He is seen getting off the bus at Shepherds Bush at 1.57pm.
He was wearing a grey beanie, a sleeveless puffa-style jacket and a beige sweatshirt, dark jeans and boots.
Detective Constable Thomas Norman from Notting Hill CID said: “This was an unprovoked attack on an innocent passenger who was on his way to work.
“It was so violent that he passed out and this could have been far worse.
Police have asked anyone with information that would help them find the attacker to call Notting Hill CID on 0208 246 0217, the non-emergency police line on 101 or Crimestoppers on 0800 555 111.
Image via Youtube