Vijay Shankar Singh was arrested from Sultanpur in the early hours today, Senior Superintendent of Police Akaash Kulhari said.
Dileep (26), a second year LLB student, was thrashed by a group on Friday following an altercation outside a restaurant. He succumbed to injuries two days later.
Four people have already been arrested in connection with the incident.
The Yogi Adityanath government came in for criticism from rival parties over the killing, with Samajwadi Party chief Akhilesh Yadav saying it showed Uttar Pradesh was in the "grip of criminal elements".