Resident Evil Zero is a third-person survival horror video game. The gameplay remains largely the same as previous entries in the series.[3] However, unlike controlling one sole character like the previous games, the player controls two protagonists throughout the game. The player may switch between police officer and medic Rebecca Chambers and convicted former Force Reconnaissance Officer Billy Coen. If they travel together, either one of them can be controlled while the other character is handled by the game's artificial intelligence (AI). The player may also control both simultaneously or split them up to explore areas separately.[3] Each character has unique abilities. Rebecca has a mixing kit which allows her to combine herbs and other chemicals, but she is weak defensively. In contrast, Billy can move heavy objects, use a lighter, and has higher defense, but cannot mix herbs (a staple ability in Resident Evil games).[4][5] The partner system is central to solving many of the game's puzzles.[6]: 17 
The characters can run as well as perform quick 180-degree turns to evade danger. The player may examine objects such as doors, other characters, and items in order to find clues to proceed through the game. Some objects can be pushed or climbed upon to investigate higher levels.[6]: 8  Items held by the characters can be examined in the inventory screen. Some items such as weapons can be equipped, and other items can be combined to create more effective items or replenish ammunition. When Rebecca and Billy are close by, they can exchange items between one-another.[6]: 10–12  Previous series installments had the player store items in boxes placed in fixed locations. Resident Evil Zero has no item boxes, and instead allows players to drop items on the floor, freeing space in the inventory momentarily until they are retrieved at a later point. The locations of dropped items are displayed on the game map.[3] The number of items that can be discarded in a room is limited.[6]: 10–12 
A bonus game, Leech Hunter, has Billy and Rebecca each collect leech charms in the mansion.