DNA studies has revealed two distinct lineages within this species, one occupying the western Atlantic and the other occupying the eastern Atlantic, Indian, and Pacific Oceans. This suggests that Indo-Pacific blacktip sharks are descended from those in the eastern Atlantic Blacktip sharks. Sharks from these two regions differ in morphology, coloration, and life history characteristics. These DNA studies, suggest that its closest relatives are the blacknose shark (C. acronotus). But more work is required to fully resolve the relationship between the blacktip shark and other Carcharhinus species.

Fossil teeth belonging to this species have been found in Delaware and Florida and dates back to 16–23 million years ago. The jaws contain 15 tooth rows on either side, with 2 symphysial teeth (at the jaw midline) in the upper jaw and 1 symphysial tooth in the lower jaw. The teeth are broad-based with a high, narrow cusp and serrated edges.

Most Blacktip sharks are found in water less than 30 m (100 ft) deep over continental and insular shelves, though they may dive to 60 m (200 ft). Favored habitats are muddy bays, island lagoons, and the drop-offs near coral reefs; they are also tolerant of low salinity and enter estuaries and mangrove swamps.

The coloration is gray to brown above and white below, with a conspicuous white stripe running along the sides. The pectoral fins, second dorsal fin, and the lower lobe of the caudal fin usually have black tips. The pelvic fins and rarely the anal fin may also be black-tipped. The first dorsal fin and the upper lobe of the caudal fin typically have black edges. Some larger individuals have unmarked or nearly unmarked fins.

This species attains a maximum known length of 2.8 m (9.0 ft), though 1.5 m (4.9 ft) is more typical, and a maximum known weight of 123 kg (271 lb).

The Blacktip shark is an extremely fast, energetic predator that is usually found in groups of varying size. There is segregation by sex and age; adult males and non-pregnant females are found apart from pregnant females, and both are separated from juveniles.

In 2007, a 9-year-old female Blacktip shark at the Virginia Aquarium & Marine Science Center was found to be pregnant with a single near-term female pup, despite having never mated with a male. Genetic analysis confirmed that her offspring was the product of automictic parthenogenesis, a form of asexual reproduction in which an ovum merges with a polar body to form a zygote without fertilization.