James Thomas, 28, of Valeside, Hertford, was found guilty of sexual assault by digital penetration by a jury at Inner London Crown Court in September this year.
The assault took place in a hotel on April 29, 2023, in the early hours of the morning.
The victim left the hotel on her on own and that afternoon called Rape Crisis.
She reported the assault to police on May 1 that year and Thomas was arrested on the same day.
Police then reviewed CCTV footage sent by the hotel to secure a prosecution.
Thomas has been sentenced to three years and a half in prison.
He also will be put on the sex offenders register.
Detective Constable Dan Lambert, at the City of London Police, said: “I want to commend the victim for the extraordinary courage she has shown in coming forward and seeing this case through to the end. I hope she feels some sense of closure and justice as a result of this conviction.
“We are committed to tackling violence against women and girls, and we take all reports of rape and sexual assault seriously and encourage victims to report their experience to police, no matter the length of time that has passed.
“We will believe you, listen and support you throughout every step of the investigation and do everything we can to bring the offender to justice.”
