Background <p>Recent research has indicated a possible connection between sleep patterns and thyroid cancer. Nevertheless, there is still a lack of evidence to support the existence of causal relationships.</p> Methods <p>We utilized a bidirectional two-sample Mendelian randomization (MR) analysis to explore the potential link between various sleep characteristics, including snoring, insomnia, sleep duration, chronotype, and daytime dozing, with thyroid cancer (TC). To conduct this analysis, we employed a range of statistical methods, including inverse variance weighted (IVW), MR Egger, weighted median, weighted mode, simple mode, and MR PRESSO. Additionally, we utilized multivariable MR (MVMR) to adjust for potential confounding factors such as body mass index (BMI), type 2 diabetes, high-density lipoprotein (HDL), and blood pressure. Besides, enrichment analysis of KEGG pathways were implemented.</p> Results <p>The results of the IVW analysis revealed that a regular chronotype had a significantly lower risk of developing thyroid cancer (OR: 0.576, 95% CI: 0.336–0.987, <i>P</i> = 0.045). This association was further supported by the weighted median method, which found an odds ratio of 0.437 with a 95% confidence interval of 0.194–0.986. Additionally, no causal relationship was found between thyroid cancer and sleep traits. MVMR method suggested that BMI and type 2 diabetes may play a role in mediating the protective effect of chronotype on TC.</p> Conclusion <p>This study indicates that chronotype may have link with thyroid cancer, highlighting regulating one's circadian rhythm, keeping slim and managing blood glucose levels for preventing thyroid cancer.</p>