The core gameplay of Leviathan is similar to that of Frozen Synapse; a planning phase during which players give movement, aiming, attacking, etc. orders which are carried out in 10-second real-time increments along with the opposing player(s) actions. These action periods are strictly defined segments of real time, such that missiles fired during the turn can be frozen in the air at the end of the turn, allowing shields to be deployed before impact.
Battles take place between fleets of pre-defined sizes based on total point value of the ships and their armaments. Within those limits, players can customize their fleets, using various hulls with different speed, vision range, and armor. Each hull has a certain number of slots into which offensive and defensive items can be installed, from basic autocannons to energy shields and long-range artillery.