The accident occurred in Gokulpuri area when Afzal and his cousin Shafeeq, who worked as vendors, were returning home from market with their carts last evening, police said.
"While they were heading towards Khajuri area, a speeding car knocked them down. Afzal sustained grievous neck and head injuries and became unconscious. Shafeeq was also seriously injured," a senior police officer said.
"Locals immediately caught hold of the car driver who was trying to flee from the spot," the officer said.
Both victims lived in Brahmpuri and had come to Delhi from Shahjahanpur in Uttar Pradesh a few months ago for work.
The accused driver has been identified as Gulshan Sharma, a resident of Rohini. He has been arrested and his car impounded. A case of causing death by negligence and rash driving has been lodged, police said.
"The accident is being probed. CCTV footage is also being checked to ascertain the sequence of events," it said.