The Irish comedian and TV presenter performed at the Kings Theatre in Southsea before heading to the One Eyed Dog for a drink on Elm Grove.
Third year sports and exercise student Naomi Clark saw the 46-year-old while out with friends.
The 21-year-old said: ‘My pals and I went into the One Eyed Dog for a drink after I had finished work.
‘My mate said to me look there is Dara O Briain and there he was sat having a drink.
‘I said to them shall we ask if he wants to party with us and so I went over and he said sure.’
The group went to Costcutters on the way to Naomi’s friend’s flat.
Naomi said: ‘He got champagne and then we went on to my friend’s whose birthday it was and said we have the best birthday surprise for you!’
Dara and the students partied till 4.30am.
Naomi said: ‘It was a really funny night and he danced with us and did karaoke and sang Backstreet Boys he was really up for a laugh.
‘One of the people whose flat it was had to get up early so we all left and I walked Dara to get a taxi and he gave me two free tickets to his show in Southsea.
‘Then he laughed about the taxi being called Aqua Cars and when I went to see him the next day the first thing he talked about was partying with us and his taxi driver named Nemo.’
Dara tweeted about his time in the city.
He wrote: ‘Hard to know if the high point of my night out in Portsmouth last night was a: attending a party in a student flat or b: the students eventually going “well, it’s getting late, and big day tomorrow, soooo....” Yes, I’m 46, what of it?’
‘Southsea: jesus, where to begin? The lonely life of the Sussex cowboy; painting is the wrong job if you hate all colours; Nemo is my taxi driver, dolphins are his engine; one snowflake, falling; I don’t want to holiday on Prison Island. #youhadtobethere’
Naomi added: ‘It will be one of those nights I will never forget.
‘It is not everyday you get to party with Dara O Briain.’