Viva Piñata is a first-person life simulation game in which the player restores and tends to a neglected garden on Piñata Island. The player uses gardening tools, such as shovels and watering cans, to plough their garden, sow seeds, create ponds, and sculpt the garden to their liking. When certain requirements are fulfilled, the garden will attract a black-and-white outline of a given piñata species. After fulfilling additional requirements, the piñata will become a resident, changing into a full-color version.
Once two piñatas of the same species are residents and their mating requirements are met, they can perform a "romance" dance. If the player successfully completes a maze minigame, the romance results in a baby piñata egg, which is delivered by a stork. The piñatas are not gendered, and hence any two piñatas of the same species can mate. Once a piñata species has successfully romanced, the player can use a candy shortcut to bypass their original romance requirements. The player can hatch the egg or send it to another player over Xbox Live. The game's antagonists include the "Ruffians" led by Professor Pester and "sour piñatas" who occasionally enter the player's garden with the sole intent of wreaking havoc: eating seeds, dropping poisonous piñata candies, and destroying objects. The player may tame sour piñatas by constructing fences around them. Weeds may occasionally sprout in the player's garden and will quickly spread to destroy vegetable rows if the player does not kill them in time.
The game features sixty types of piñatas. Certain animals are "piñatavores", and must eat other piñatas to become residents or reproduce. A food chain (referred to as the doughnut of life) exists, with a number of piñata species having one or two others that are considered prey. When such piñatas are visiting the garden, they devour garden residents to satisfy their residency requirements. Once piñatas are residents, they will not eat each other unless instructed to do so by the player, although fights can break out between residents who do not share the predator–prey relationship. Piñatas die when they are broken open, either from another piñata's predaciousness, the hit of the player's or Professor Pester's shovel, or following an extended illness. Dead piñatas forfeit their equipped accessories. Players were also able to trade their piñatas with other players over the internet via Xbox Live.