Following the style of its predecessors, the game uses a battle system different from that of typical fighting games. Choosing from a variety of characters, one to four players fight on various stages, trying to knock their opponents off the screen.

Instead of using health bars like those used in most fighting games, percentage displays are employed. These start at 0%, and increase as the characters take damage up to 999%. As a character's percentage goes up, the character flies farther back when hit.

When a character is knocked beyond a stage's boundary and disappears from the screen, the character loses either a life or a point depending on the mode of play.

The game can be played using the Wii Remote on its side, the Wii Remote and Nunchuk together, the Classic Controller, or the GameCube controller, for a total of four possible control styles.

Stages are arenas that are generally based on levels from the various represented game series of Super Smash Bros. Stages range from floating platforms to moving areas where the characters must stay within the field of play. Each stage has a boundary that cannot be passed, or the character will be "KO'd", thus losing a life or losing a "point".

Brawl also allows players to create their own stages using a variety of options in a mode called Stage Builder. Players can save their stages to an SD card or the internal memory of the Wii console.

Stages can also be sent to registered friends. Through Nintendo Wi-Fi Connection, players are able to submit their creations daily to Nintendo, and receive a daily stage from the service.

Super Smash Bros. Brawl features a new Adventure Mode titled "The Subspace Emissary". This mode features unique character storylines along with numerous side scrolling levels and multiple bosses to fight, as well as CG cut scenes explaining the storyline.

"The Subspace Emissary" features a new group of antagonists called the Subspace Army, who are led by the Ancient Minister. Some of these enemy characters appeared in previous Nintendo video games, such as Petey Piranha from the Mario series and a squadron of R.O.B.s based on classic Nintendo hardware.

Super Smash Bros. Brawl allows players to play against distant opponents through the use of Nintendo Wi-Fi Connection. Online multiplayer games can be played either with registered friends or with other randomly selected participants.

The players' nicknames will be displayed during multiplayer matches. Additionally, players can converse with up to four phrases that are set by the player beforehand. The four phrases correspond to the characters' taunts and will appear in speech bubbles above the characters. It has been stated that these names and phrases will not be displayed in random-player matches.

A Spectator mode allows players to watch matches from players who have enabled the 'Allow Spectators' option, and bet on the outcome using coins earned within the game. The winner of the bet receives a jackpot of coins.

The cast of characters includes various returning characters from Super Smash Bros. Melee and a variety of newcomers.

Some returning characters have been updated or refined since their last appearance, either in terms of appearance, fighting capabilities, or both. For example, Link and Fox have taken on new designs from more recent titles, while Samus has gained the ability to change into a new form, "Zero Suit Samus".