Zakaria Mohammed, 32, inflicted wounds to the back of the 21 year-old passenger's head after deliberately blocking him in on the early morning service.
British Transport Police (BTP) have described it as a “sickening” attack, which left the victim with bleeding wounds.
Mohammed, of The Coppice, West Drayton, pleaded guilty to causing actual bodily harm, sexual assault and false imprisonment.
He also admitted breaching the conditions of a previous Sexual Harm Prevention Order (SHPO), which was made after previous offending.
Mohammed was jailed for one year and eight months at Reading Crown Court and placed on the sex offenders register for 10 years.
He was also made the subject of a 10-year SHPO.
Shortly before 8.30am on Saturday, March 24, Mohammed sat directly opposite the victim at a table in an otherwise empty carriage.
The pair made small talk until Mohammed, who had clearly been drinking and was carrying a half empty bottle of wine, sexually assaulted the victim.
He moved to deliberately sit next to the victim, who attempted to leave his seat when the train reached Reading station.
When he asked Mohamed to move so he could leave the defendant refused, leaving the victim with no other option than to crawl under the table to escape.
However, as he was doing so, Mohammed repeatedly hit him over the head with his wine bottle.
On leaving the train the victim reported what had happened and realised he was bleeding heavily from cuts to his head.
Mohammed was arrested by BTP officers as he approached the barriers to leave the station and was found to be in breach of a previous SHPO forbidding him from travelling on public transport without paying for a ticket.
BTP Detective Constable Lauren Pace said: “This was a truly sickening assault on a young man who was understandably terrified.
“Mohammed is a dangerous individual who saw nothing wrong with forcing himself upon the victim.
“Quite rightly he has been jailed as a result of our investigation and issued with a SHPO which will hopefully prevent him from attacking anyone else.”
