Three people were injured outside Sugar Hut in Brentwood - as featured in TV show The Only Way is Essex - when a car mounted the pavement during a brawl.
The fight early on Sunday involved more than 20 people, police said.
Essex Police said a 32-year-old man from West Drayton in west London, was being questioned along with a 26-year-old woman.
The woman, from Hornchurch, east London, was arrested on suspicion of assisting an offender.
One of the people hit by the car - a blue Audi - is in a critical condition in hospital, police said.
The other victims, a man and a woman, have been discharged.
Police are still appealing for anyone with information about the hit-and-run, which happened at 03:10 BST on Sunday, to contact Brentwood's major investigations team or Crimestoppers.
A man has been arrested on suspicion of attempted murder following a hit-and-run outside an Essex club.