Deadlight is a 2.5D sidescroller in which the player character can move only from left-to-right and right-to-left, and is unable to enter any environments off the aligned path. The game consists of puzzles which the player must solve as he attempts to avoid the many "Shadows" (zombies) he encounters. Players are advised to avoid Shadows as much as possible, and try not to engage them in combat. When combat is unavoidable, the player can use melee attacks with a fire axe, which consumes stamina, or later, he can use a revolver, and then a shotgun, although ammunition for both weapons is extremely limited. The player also gains access to a slingshot. However, this cannot be used in combat, and is instead used for solving puzzles. There are only a small number of occasions when combat is completely necessary however, and throughout the game, the emphasis of the gameplay remains strongly on avoiding Shadows, not confronting them.

The character begins with three health points which can be replenished by using first aid kits. The number of health points can increase by a single point if the player can find power-ups. Running and melee combat deplete the player's stamina meter, which causes the screen to blur and the player to stop moving so as to get his breath back. As with the health meter, the amount of available stamina can also be increased by power ups. Unlike health, however, the stamina meter refills over time.

The game contains many hidden collectable items strewn throughout its levels. Some are entries from the player's diary, revealing more about his backstory. Others are personal memorabilia lost by people in the early days of the outbreak. A recurring collectible comes in the form of identification cards, all of which feature the name of serial killers (such as John Wayne Gacy, Albert DeSalvo, Aileen Wuornos and Jeffrey Dahmer), although the photo ID on the cards feature members of Tequila Works' staff.