Marc Martin, 22, and Matt Preece, 21, died after the BMW hit a tree and flipped on to its roof in High Beeches Lane, Handcross, on 17 December.
Two other passengers, a girl aged 16 and the 20-year-old driver, were hurt. The crash happened at about 22:00 GMT.
Sussex Police said the man was being questioned on suspicion of two counts of causing death by dangerous driving.

Betty Boylan's relatives put a camera in her room at Bupa's Perry Locks home in Birmingham after they found bruises on her, a court heard.
Bina Begum, 49, was given a 12-month community order after admitting ill treating and neglecting Mrs Boylan.
Bupa said she had been dismissed and her actions were "unacceptable".
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Noreen Ashraf, prosecuting, told Birmingham Magistrates' Court Mrs Boylan was "left slumped in her chair with significant leaning to her side" on 15 September.
She said: "The complainant does want to move her arm. The defendant forces her arm and pushes her back into the chair.
"The complainant cries out. She slams her head back into the chair with significant force to cause the chair to rock."
Mrs Boylan's daughter, Bernadette Jarvis, said: "To a vulnerable person as well who can't say anything, there's just no words to explain what she's done to be quite honest."
The family also captured images of deodorant being sprayed in the woman's face, which is under investigation.
West Midlands Police said a 43-year-old woman had been voluntarily interviewed "in connection with an assault on a 77-year-old woman in a care home" and inquiries were ongoing.
Bupa Care Services director of quality Vivienne Birch said the apparent actions "of these individuals are unacceptable".
She said they were "immediately removed" from the home and they had since been formally dismissed.
"We were shocked and saddened by the footage. We're deeply sorry this happened and the distress it has caused Mrs Boylan's family.
"We're proud of the care our staff provide and do not tolerate behaviour like this at any of our homes."
The family had other images of a male patient in Mrs Boylan's room.
In response, the Bupa Care Services director of quality said: "Our night staff found the resident sitting in the wrong bedroom while doing their regular checks and he was safely taken back to his room.
"He had only been at the home for a few days and was confused by his surroundings."
Begum, of Teddington Grove, Perry Barr, who admitted wilful ill treatment and neglect, said she accepted her actions were "reckless rather than intentional or deliberate" in a letter read out in court.
She was also ordered to carry out 40 hours of unpaid work and fined £270.
Nazia Jan, defending, said Begum was "very, very remorseful".
She said: "It's cost her her chosen career... This act was completely out of character, blemished her good character and caused her unquantifiable distress."
The driver of a car involved in a single-vehicle crash in West Sussex in which two men died has been arrested.
[NEXT_CONCEPT]
A care worker was caught slamming the head of a 77-year-old woman with dementia into a chair on secret CCTV installed by her family.