Food waste (FW) has been increasingly recognized as a severe environmental, social, and economic problem. Therefore, it should be tackled innovatively by analyzing and synthesizing existing solutions. This study aims to achieve a comprehensive understanding of different social innovation measures adopted for reducing FW using a systematic literature review. After locating, collecting, evaluating, and analyzing 50 publications from four databases, we conclude that social innovation activities such as digital food-sharing platforms, social supermarkets, solidarity stores, and food rescue hubs are widely deployed in different FW reduction processes. Based on the findings, we synthesized several research gaps and proposed corresponding future research directions related to research methodology, country, food redistribution, food rescue, food donation, and food sharing. These directions include conducting research to develop suitable key performance indicators to evaluate the performance of digital food-sharing platforms, linking with specific theory to conduct empirical research on partnership analysis regarding social supermarkets, and investigating the structure of multiplex relations among different participants in the food rescue activities using social network analysis. We suggest that more keywords should be scrutinized and included when searching publications in future research as keyword selection is subjective.