Poor sleep is increasingly seen as an issue of public health concern. In recent years, there has been growing interest in protein as a route to improve sleep outcomes; however, the evidence is limited and inconclusive. To examine, using a systematic review and meta-analysis, the effect of increased protein intake (≥1 g/kg//d, ≥25% of total energy intake, or protein supplementation of ≥10 g/d/) on sleep outcomes in adults. On November 30, 2021, 5 electronic databases were searched to identify relevant randomized controlled trials (PubMed, Cochrane, Embase, Web of Science, and CINAHL Plus). Risk of bias was assessed using the Cochrane Risk-of-Bias tool, version 2.0. Five sleep outcomes were included in this systematic review (sleep quality [SQ], sleep latency [SL], sleep efficiency [SEff], sleep time [ST], wake episodes, and other sleep outcomes) and 4 in the meta-analysis (SQ, SL, SEff, and ST). The quality of evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation approach. Twelve intervention studies reported on in 10 articles were included. The qualitative analyses showed that increased protein consumption has little influence on sleep outcomes. Only subjective SQ was positively associated with protein consumption in a few studies. Meta-analyses also showed no significant effect of increased protein intake on sleep outcomes (number of studies for SQ, ST, SL, and SEff: 8, 8, 7, and 6, respectively), with very low certainty of evidence. However, results from sensitivity analyses, excluding high-risk studies, suggest a small effect on SQ in favor of high protein intake (mean difference, -4.28; 95%CI, -7.77, -0.79; on a scale from 0 to 100). This systematic review and meta-analysis indicate there is no clear relationship between increased protein intake and sleep. However, the strength of the evidence is low and more randomized controlled trials that focus on this specific research question are warranted. Systematic Review Registration: PROSPERO registration no. CRD42020196021.