Ioachim Ciobanu of Chertsey Road approached a 22-year-old woman as she stood waiting to board a Metropolitan line train at Baker Street station and touched her inappropriately, police said.
The "atrocious act" was reported by the victim to a female member of staff at the station on October 9, who then took her to the station control room and called the police.
With the use of CCTV, Ciobanu's footsteps were traced on camera and he was identified by the young woman to the police when they arrived at the scene.
Officers arrested the man and he was later charged with sexual assault.
He received a four month suspended sentence for two years and has been placed on the Sexual Harm Prevention Order for five years.
The 29-year-old pleaded guilty to the sexual assault charge and was sentenced at Blackfriars Crown Court on Monday (December 19).
British Transport Police investigating officer, DC Dean Percival, said: “This was serious and a truly abhorrent incident.
"The victim was left violated by the action of Ciobanu.
"British Transport Police takes all sexual offences seriously and I would like to thank the victim for coming forward and reporting this to us so that this man was able to be put through the court system and convicted for his atrocious act."
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