It is becoming increasingly difficult to ignore circular and sustainable economies. A traditional chain transits to a dual-channel supply chain, extending its online channel for more customers, and keeping its offline channel so as to reduce resource utilization for sustainable business. However, there exists some conflict between offline and online channels, such as the showrooming effect (i.e., customers visit an offline store to experience products but then buy them online with a lower price). This work studies a three-echelon book dual-channel supply chain involving an author, an online publisher and an offline retailer. Based on Stackelberg game theory, it investigates the optimal pricing solutions and the optimal retailer’s service effort level with two copyright models and considers the showrooming effect based on either decentralized or centralized decision-making. Afterwards, it develops a cost-sharing contract to make them achieve Pareto optimality. Furthermore, this research studies the influence of the showrooming effect on the optimal decisions and the profits of each member through theoretical and numerical analyses. The findings show that a well-designed contract can lead dual-channel members to cut down the negative impact of the showrooming effect and realize the win–win situation. Finally, it proposes some managerial insights and possible directions for the future.