- Jim Hawkins: The first-person point of view, of almost the entire novel. Jim is the son of an innkeeper near Bristol, England, and is probably in his early teens. He is eager and enthusiastic to go to sea and hunt for treasure. He is a modest narrator, never boasting of the remarkable courage and heroism he consistently displays. Jim is often impulsive and impetuous, but he exhibits increasing sensitivity and wisdom.
- Dr. Livesey: The local doctor. Dr. Livesey is wise and practical, and Jim respects but is not inspired by him. Livesey exhibits common sense and rational thought while on the island, and his idea to send Ben to spook the pirates reveals a deep understanding of human nature. He is fair-minded, magnanimously agreeing to treat the pirates with just as much care as his own wounded men. As his name suggests, Livesey represents the steady, modest virtues of everyday life rather than fantasy, dream, or adventure.
- Long John Silver: The cook on the voyage to Treasure Island. Silver is the secret ringleader of the pirate band. His physical and emotional strength is impressive. Silver is deceitful and disloyal, greedy and visceral, and does not care about human relations. Yet he is always kind toward Jim and genuinely fond of the boy. Silver is a powerful mixture of charisma and self-destructiveness, individualism and recklessness. The pegleg Silver was based in part on Stevenson's friend and mentor William Ernest Henley.
- Captain Smollett: The captain of the voyage to Treasure Island. Captain Smollett is savvy and is rightly suspicious of the crew Trelawney has hired. Smollett is a real professional, taking his job seriously and displaying significant skill as a negotiator. Like Livesey, Smollett is too competent and reliable to be an inspirational figure for Jim’s teenage mind. Smollett believes in rules and does not like Jim’s disobedience; he even tells Jim that he never wishes to sail with him again.
- Squire Trelawney: A local wealthy landowner; his name suggests in Cornwall (a traditional English rhyme states "By Tre Pol and Pen, Ye shall know all Cornishmen"). Trelawney arranges the voyage to the island to find the treasure. He is associated with civic authority and social power, as well as with the comforts of civilized country life (his name suggests both “trees” and “lawn”). Trelawney’s street smarts, however, are limited, as the ease with which the pirates trick him into hiring them as his crew demonstrates.
- Billy Bones: The old seaman who resides at Jim’s parents’ inn. Billy, who used to be a member of Silver’s crew, is surly and rude. He hires Jim to be on the lookout for a one-legged man, thus involving the young Jim in the pirate life. Billy’s sea chest and treasure map set the whole adventure in motion. His gruff refusal to pay his hotel bills symbolizes the pirates’ general opposition to law, order, and civilization. His illness and his fondness for rum symbolize the weak and self-destructive aspects of the pirate lifestyle. He dies of a stroke as a result of a combination of drinking too much rum and the double shock of seeing Blind Pew and the realization that Long John Silver has tracked him down.
- Alan: A sailor who does not mutiny. He is killed by the mutineers for his loyalty and his dying scream is heard by several.
- Allardyce: One of the six members of Flint's Crew who, after burying the treasure and silver and building the blockhouse on Treasure Island, are all killed by Flint. His body is lined up by Flint as a compass marker to the cache. According to The Adventures of Ben Gunn, his first name was Nick, he was surgeon on Flint's crew, and Ben Gunn was his servant and friend from back home.
- Job Anderson: The ship's boatswain and one of the leaders of the mutiny. He participates in the storming of the blockhouse, and is killed by Gray while attacking Jim. Possibly one of Flint's old pirate hands (though this is never stated). Along with Hands and Merry, he tipped a Black Spot on Silver and forced Silver to start the mutiny before the treasure was found.
- Mr. Arrow: The first mate of the Hispaniola. He drinks despite there being a rule about no alcohol on board and is useless as a first mate. He mysteriously disappears before they get to the island and his position is filled by Job Anderson. (Silver had secretly given him access to alcohol and he fell drunkenly overboard on a stormy night.)
- Black Dog: Formerly a member of Flint's pirate crew, later one of Pew's companions who visits the Admiral Benbow to give Billy Bones the Black Spot. Spotted by Jim and chased by two of Silver's men, but disappears from sight. Two fingers are missing from his left hand.
- Captain Flint: John Flint, the fictional pirate Captain of the Walrus. After robbing and looting towns and ships among the Spanish Main, in August 1750 he took six of his own crew onto Treasure Island. After building a stockade and burying the bulk of his looted treasure, he killed all six men. In July 1754 he died at Savannah, Georgia, of Cyanosis, caused by drinking too much rum. While dying he gives his treasure map to Billy Bones. Long John Silver's parrot is named after Captain Flint. Several members of his crew figure in the story: William "Billy" Bones, the ship's first mate; Long John Silver, the ship's quartermaster; Israel Hands, the ship's chief gunner; Allardyce, used as Flint's "pointer" to the treasure; Job Anderson, the Hispaniola boatswain and mutineer; Dirk, one of Pew's henchmen in the assault on the Admiral Benbow inn; Black Dog, another of Pew's henchmen in the assault on the Admiral Benbow inn; Benjamin Gunn, the island maroon; John, a Hispaniola mutineer, possibly one of Pew's henchmen on the assault on the Admirial Benbow inn; Tom Morgan, a Hispaniola mutineer; Blind Pew, the blind murderous beggar; and an unnamed mutineer of the Hispaniola marooned with Morgan and Johnson on Treasure Island.
- Abraham Gray: A ship's carpenter on the Hispaniola. He is almost incited to mutiny, but remains loyal to the Squire's side when asked to do so by Captain Smollett. He saves Hawkins' life by killing Job Anderson during an attack on the stockade, and he helps shoot the mutineers at the rifled treasure cache. He later escapes the island together with Jim Hawkins, Dr. Livesey, Squire Trelawney, Captain Smollett, Long John Silver, and Ben Gunn. He spends his part of the treasure on his education, marries, and becomes part owner of a full-rigged ship.
- Benjamin "Ben" Gunn: A former member of Flint's crew who became half insane after being marooned for three years on Treasure Island, having convinced another ship's crew that he was capable of finding Flint's treasure. Helps Jim by giving him the location of his homemade boat and kills two of the mutineers. After Dr. Livesey gives him what he most craves (cheese), Gunn reveals that he has found the treasure. In Spanish America he lets Silver escape, and in England spends his share of the treasure (£ 1,000) in 19 days, becoming a beggar until he becomes keeper at a lodge and a church singer "on Sundays and holy days".
- Mr. Dance: Chief revenue officer (titled: Supervisor) who ascends with his men upon the Admiral Benbow, driving out the pirates, and saving Jim Hawkins and his mother. He then takes Hawkins to see the squire and the doctor.
- Dogger: One of Mr Dance's associates, who doubles Hawkins on his horse to the squire's house.
- Israel Hands: The ship's coxswain and Flint's old gunner. He is killed on the Hispaniola by Jim Hawkins when he tries to murder him.
- John: A mutineer who is injured while trying to storm the blockhouse. He is later shown with a bandaged head and ends up being killed at the rifled treasure cache.
- Mr. and Mrs. Hawkins: The parents of Jim Hawkins. Mr. Hawkins dies shortly after the beginning of the story.
- John Hunter: The other manservant of Squire Trelawney. He also accompanies him to the island, but is later knocked unconscious at an attack on the stockade. He dies of his injuries while unconscious.
- Dick Johnson: The youngest of the mutineers, who has a Bible. The pirates use one of its pages to make a Black Spot for Silver, only to have him predict bad luck on Dick for sacrilege. Soon becoming mortally ill with malaria, Dick ends up being marooned on the island after the deaths of George Merry and John.
- Richard Joyce: One of the manservants of Squire Trelawney, he accompanies him to the island. He is shot through the head and killed by a mutineer during an attack on the stockade.
- George Merry: A treasonous and hostile member of Silver's crew, who disobeys orders and occasionally challenges Silver's authority. He launches the mutiny prematurely, forcing Long John to flee to the island with Jim as an improvised hostage. With Anderson and Hands he forces Silver to attack the blockhouse instead of waiting for the treasure to be found. Later killed at the empty cache just as he is about to kill both Silver and Hawkins.
- Tom Morgan: An ex-pirate from Flint's old crew. He ends up marooned on the island with Dick and one other mutineer.
- O'Brien: A mutineer who survives the attack on the boathouse and escapes. He is later killed by Israel Hands in a drunken fight on the Hispaniola.
- Pew: An evil and deadly blind beggar who is accidentally trampled to death by the horses of revenue officers riding to assist Jim Hawkins. Silver claims Pew spent his share of Flint's treasure (£ 1,200) in an entire year and that for two years until his accident at the "Admiral Benbow" he begged, stole, and murdered. Stevenson avoided predictability by making the two most fearsome characters a blind man and an amputee. In the play Admiral Guinea (1892), Stevenson gives him the full name "David Pew". Some film adaptations call him "Blind Pew". Stevenson's novel Kidnapped (1886) also features a dangerous blind man.
- Tom Redruth: The gamekeeper of Squire Trelawney, he accompanies the Squire to the island but is shot and killed by the mutineers during an attack on the stockade.
- Tom: An honest sailor. He starts to walk away from Silver who throws his crutch at him, breaking Tom's back. Silver kills Tom by stabbing him twice in the back.
Among other minor characters whose names are not revealed are the four pirates who were killed in an attack on the stockade along with Job Anderson; the pirate killed by the honest men minus Jim Hawkins before the attack on the stockade; the pirate shot by Squire Trelawney when aiming at Israel Hands, who later died of his injuries; and the pirate marooned on the island along with Tom Morgan and Dick.
Stevenson deliberately leaves the exact date of the novel obscure, Hawkins writing that he takes up his pen "in the year of grace 17—." Stevenson's map of Treasure Island includes the annotations Treasure Island 1 August 1750 J.F. and Given by above J.F. to Mr W. Bones Maste of ye Walrus Savannah this twenty July 1754 W B. The first of these two dates is likely the date at which Flint left his treasure at the island; the second, just prior to Flint's death. Flint is reliably reported to have died at least three years before the events of the novel (the length of time that Ben Gunn was marooned). Other dates mentioned include 1745, the date Dr. Livesey served as a soldier at Fontenoy and also a date appearing in Billy Bones's log.