Objective To investigate the causal relationship between Helicobacter pylori (Hp) infection and immune thrombocytopenia (ITP) using Mendelian randomization (MR), as well as the association between Hp infection and chronic ITP (cITP) through a clinical study. Methods The datasets from genome-wide association studies were used to select the single nucleotide polymorphism loci significantly associated with Hp infection as genetic instrumental variables. The MR analysis model was used to investigate the causal relationship between ITP and Hp infection. A retrospective analysis was conducted on the medical data of 316 children with newly diagnosed ITP at the First Affiliated Hospital of Xinjiang Medical University from January 2020 to December 2023. The children were followed up for 1 year, and a multivariate logistic regression analysis was used to investigate the risk factors for cITP. Results The inverse variance weighted analysis revealed that Hp infection was significantly associated with an increased risk of ITP (OR=1.280, 95%CI: 1.098-1.492, P=0.002). There was no heterogeneity or pleiotropy in this MR study (P>0.05), and the model was stable. The "leave-one-out" sensitivity analysis verified the reliability of the results. The multivariate logistic regression analysis demonstrated that Hp infection was an independent risk factor for progression to cITP (OR=7.916, 95%CI: 3.327-18.832, P<0.001). Conclusions Hp infection is a risk factor for the onset of ITP and is an independent risk factor for cITP in children.