The following refers to the original Famicom/NES version. For changes in subsequent remakes, see the section on Development.

Gameplay in Final Fantasy is similar to that of many other console role-playing games. The player controls a party of four player characters, called Light Warriors (or "Warriors of Light" in later editions), who explore towns and dungeons as they travel across the world map. The goal of the game is to defeat four major enemies called Elemental Fiends or Fiends of Chaos. Along the way, the player travels to towns where he or she may shop, acquire information, and rest. While traveling, the player encounters monsters which must either be combated or fled from. Winning battles earns the player experience points, which strengthen player characters, and gold (gil in later versions) currency to buy new equipment.

The player begins Final Fantasy by creating the Light Warriors. As is typical of computer role-playing games of the era, player characters are passive participants in the story, with their names and abilities relevant only during battle. Characters are determined by four-character (i.e. four-letter) names (more in later editions), certain numerical attributes, and their class. A character's most basic attribute is its level, which is numbered between one and fifty. (The maximum is ninety-nine in later editions.) A character's level is determined by how much experience it has, and higher level characters are more powerful than lower level characters. Gaining a level increases the character's attributes, such as their maximum hit points (HP). HP represents a character's remaining health, and when a character reaches zero HP, they die. Additional attributes such as "Strength" govern other aspects of the character.

Each character has a character class, which affects the character's attributes and abilities. There are six classes, three of which are physically oriented and three of which are magically oriented. During the game, the player has the option of completing a quest which changes and upgrades each character to a different and more powerful class. With the exception of this upgrade, character classes cannot be changed once the game has begun.

The "Fighter" ("Warrior" in later editions) uses heavy weapons and armor, and can be upgraded into a "Knight", who is also able to use low-level White Magic spells. The "Black Belt" (or "Monk") is skilled at fighting armorless while empty-handed and upgrades to a "Master." The fast and agile "Thief" can upgrade into a "Ninja", which may use low-level Black Magic spells. Of the three magical classes, the "Red Mage" is a decent fighter and can use a mixture of White and Black Magic. The Red Mage upgrades to a "Red Wizard" who can use more powerful equipment and spells. The "White Mage" can cast defensive and curative spells and upgrades to a "White Wizard," while the "Black Mage" can cast offensive spells and upgrades to a "Black Wizard." Both the Black and White Mages/Wizards are comparatively weak at physical offense compared to the other characters in exchange for their powerful magic.

Combat

The Light Warriors face off against Lich, Fiend of Earth (NES version shown)

Battles in the game are turn-based. At the beginning of each turn, the player selects an action for each player character, with the options being direct attacks, casting spells, drinking potions, using magical items, or running. Once the player has chosen actions for each player character, the player characters and monsters begin battling. Participants move one at a time in a randomly determined order.

In the original NES version, it was not possible to select a new enemy to attack once actions had begun; if the character had chosen to attack an enemy who had been defeated earlier in the round, then the attack was ineffective, and the character did nothing. This was changed in later versions.

Battles continue until one side either flees or is defeated. If the party wins, the characters gain experience and gold. If the party flees, they return to the map. If the party dies, the game is over.

Customization

Final Fantasy contains a variety of weapons and armor; new equipment can make the Light Warriors more powerful in combat. Each Light Warrior has eight inventory slots, with four to hold weapons and four to hold armor. Each character class has restrictions on what weapons and armor it may use. Additionally, some weapons and armor are magical; if used during battle, some of these items will cast spells. Other magical artifacts provide protection, such as from certain dangerous spells.

There are six types of weapons: Swords, Daggers, Axes, Hammers, Staves, and Nunchaku. Warriors may also fight bare-handed; however, only the Black Belt/Master may do so effectively. The type of a weapon mainly determines its associated graphics, but also indicates which classes are more likely able to use that weapon. For example, a Black Belt is able to equip nunchaku but cannot equip axes. Each weapon has three statistics: damage, chance to hit bonus, and critical hit chance. Certain weapons are also more effective against monsters of particular types or monsters weak against particular elements. In the original NES version, these properties and the critical hit chance were not used due to bugs, but these were fixed for later revisions. While four weapons may be held, only one weapon may be used at a time.

In addition to weapons, there are four types of armor: Armor (Cuirasses, Robes, Bracelets), Helmets, Gauntlets, and Shields. Unlike weapons, a piece of armor's type is very important. A character may wear up to four different pieces of armor at once, but only one of each type. Each armor has two statistics: a damage absorption bonus and an evade penalty. Certain kinds of armor also grant resistance to particular categories of magic.

At shops, the Light Warriors can buy items to help themselves recover while they are traveling. Up to 99 of each item may be carried at one time. Items available include "Potions", which heal player characters or remove an ailment such as poison or stoning; "Tents" and "Cabins", which can be used on the world map to heal the player and optionally save the game; and "Houses", which additionally recover the party's magic after saving. Additional special items may be gained during or at the completion of quests.

Many character classes are able to use magic, which is divided into "white" defensive magic and "black" offensive magic. Spells are classified by a level between one and eight, with, in most cases, higher level spells being more powerful than lower level spells. There are four white magic and four black magic spells of each level. Characters may learn up to three spells of each level by purchasing them at shops in towns. White wizards are capable of learning all white magic spells, and black wizards are capable of learning all black magic spells. Other classes have various restrictions on the spells they can learn. In the original NES version, once a spell has been learned it cannot be forgotten. This was changed in some later revisions.

The original NES version of the game allowed each magic-user "charges" for each level of spells; spells of a given level could only be cast as many times as the user had charges. As a character's level increased, more charges were gained. This system closely resembles the spell-casting system in Dungeons & Dragons. In some later revisions of the game, this system was replaced by MP (Magic Points).