Tahir Nazir, 40, of Glasgow, also targeted students in Manchester where he tried to rape a sleeping woman.
Manchester Crown Court heard he had a sexual obsession with students and repeatedly tried to enter their rooms during a tour of university locations.
He was found guilty of sexual assault, attempted rape and trespass offences.
The court heard Nazir was caught "on top" of a very drunk student after he broke into a house in Cathays, Cardiff, on 22 September, through a bathroom window.
On 1 November, a woman in Hulme, Manchester, said she woke to find him "licking her neck".
He was arrested on 6 November after women in a shared house in Fallowfield, Manchester, became concerned someone was trying to open the doors of their rooms in the early hours of the morning.
Nazir had denied claims his trips to Inverness, Aberdeen, Dundee, Edinburgh, Glasgow, Manchester, Oxford, Bristol and Cardiff had a sexual purpose.
Instead, he told the court he loved driving and was "inspired by Gothic architecture".
He admitted having a fake university ID, which he said he used for discounts, and Viagra in his car, which he said gave him energy for clubbing.
The case was adjourned for sentencing in May.
A prowler who broke into a house in Cardiff looking for students to sexually assault has been found guilty of a string of sexual offences.