The solid-phase conversion mechanism in lithium–sulfur (Li–S) batteries has emerged with many attractive advantages such as avoiding the parasitic “shuttle effect” of soluble polysulfides and allowing lean electrolyte operating conditions. Electrolyte regulation could be a vital strategy for taking full advantage of solid-phase conversion to realize high-energy Li–S batteries. This review aims to provide a comprehensive overview of the role of electrolyte regulation in promoting solid-phase conversion, thereby preparing high-energy Li–S batteries in liquid, quasi-solid-state, and solid-state media. The work introduces the significance and historical development roadmap of solid-phase conversion in Li–S batteries and explores a design strategy for functional electrolytes based on working mechanisms. Furthermore, it outlines the challenges and opportunities in developing modern Li–S batteries governed by solid-phase conversion. We aim to provide insights and design principles for regulating electrolytes to solve the challenges presented in Li–S batteries, and we hope to provide readers with guidelines for the development and utilization of high-energy Li–S batteries.