The main gameplay for Fortnite Battle Royale follows the battle royale genre's standard format. The game normally is played either with each player on their own, or in a squad of two to four players, with up to 100 players participating each round. The round starts with players, weaponless, skydiving from floating buses ("Battle Bus") then deploying a glider onto a region of land. The island's fixed layout includes several landmarks and locations such as "Loot Lake", "Tilted Towers", and "Retail Row" that are mostly ghost towns, while a random distribution of weapons, shields, and other combat support features can be found by searching buildings and other sites. The goal is to be the last player or team alive by eliminating or avoiding other players.

When playing in solo modes, players are immediately eliminated when they exhaust their health, while in squad modes, downed players can crawl around while bleeding out; they can be eliminated immediately by an opponent or revived by a squadmate to help them up. Initially, when the game launched, eliminated players were out of the match, but starting with updates in April 2019, squadmates can attempt to revive a downed player at various "Reboot vans" scattered around the map, which are few and far between and in the open, making it a risk to respawn a squadmate. Over time, the game's safe zone (representing the eye of a storm), decreases in size, and players caught outside the zone will take damage. This directs the surviving players into tighter spaces, forcing player encounters. Supply drops will spawn in random locations during a match, providing random weapons and items. Like in the original Fortnite game, Fortnite Battle Royale is primarily played in a third-person perspective.

Fortnite Battle Royale's primary distinction from other battle royale games is the building system, which originated from the original Fortnite survival game. Nearly all objects in the environment can be destroyed and harvested for materials (wood, stone, and metal), which can then be used to build fortifications of limited durabilities, such as walls, ramps, floors, and roofs, which can be used to help traverse the map, protect the player from gunfire, or slow down progression of other players. Weaker pieces can be destroyed in a few hits, but can be built quickly, while stronger pieces can withstand more punishment, but take longer to build.