The player, controlling a sorcerer known only as Dana, must overcome unlimited enemy spawning, challenging level designs, a countdown timer, instant death from any physical contact with enemies, and limited ways to dispatch enemies.

Dana is sent to retrieve Solomon's Key to restore the world to light from demons that were accidentally released. The object of the game is to advance through the 50 rooms of "Constellation Space" by acquiring a key to the door that leads to the next room before a timer runs out. The game incorporates elements of the platform shooter genre. Dana can run, jump, create or destroy orange blocks adjacent to him as well as create fireballs to destroy demons. The orange blocks can also be destroyed by hitting them with the character's head twice. Along the way Dana can acquire items to upgrade his firepower and extra lives, as well as items that award bonus points and unlock hidden rooms. With certain items, Dana must make, then break blocks (sometimes in a certain manner) to make these appear.

In the NES version, a "GDV" (Game Deviation Value) score also appears at the game over screen. The score uses a weighted composite of several factors (like levels completed, items found, time and points) which gives the player a good idea of how well the last game was played. The higher the GDV, the better the game.

Solomon's Key has many hidden items and secret levels that are hard to find which enhances the reward for playing. The ending slightly changes depending on which secret levels, if any, the player finds and completes.