Ben Pountney, 30, and of Swallows Meadow, Solihull, appeared at Warwick Crown Court on December 5, 2022 where he pleaded guilty to one count of sexual assault.
On Thursday, January 26 he was sentenced at the same court to 20 months imprisonment.
He was also handed a ten-year Sexual Harm Prevention Order and ordered to sign the Sex Offenders Register for ten years.
The court heard how on Tuesday, October 13, 2020, the 17-year-old victim was travelling on a quiet train from Stratford-upon-Avon when a man boarded a few stops later and sat opposite her.
She noticed the man looking at her and after a short while he began speaking to her.
He persistently asked about the shoes she was wearing and her shoesize.
He stated that he wanted to buy a similar pair for his niece, while getting closer to the girl and leaning in towards her.
He then sexually assaulted her and got off the train.
Following a number of enquiries and a media appeal to the public, Pountney was later identified and arrested.
Police Sergeant Daniel Hart, investigating officer in the case, said: “Pountney is a vile offender who targeted a lone teenager and subjected her to a distressing sexual assault.
"His sleazy behaviour is a prime example of the harassment and intimidation of women and girls which we are dedicated to tackling on the network.
"It simply won’t be tolerated, and we will bring offenders to justice.
"If you are a victim of, or a witness to, a sexual offence on the railway - I urge you to report it to BTP by texting 61016 or via the Railway Guardian app. We will always take you seriously".