OBJECTIVE: Previous genetic and clinical analyses have associated lower lipoprotein(a) and LDL cholesterol (LDL-C) with greater risk of new-onset type 2 diabetes (NOD). However, PCSK9 inhibitors such as alirocumab lower both lipoprotein(a) and LDL-C without effect on NOD. RESEARCH DESIGN AND METHODS: In a post hoc analysis of the ODYSSEY OUTCOMES trial (NCT01663402), we examined the joint prediction of NOD by baseline lipoprotein(a), LDL-C, and insulin (or HOMA-insulin resistance [HOMA-IR]) and their changes with alirocumab treatment. Analyses included 8,107 patients with recent acute coronary syndrome on optimized statin therapy, without diabetes at baseline, assigned to alirocumab or placebo with median follow-up 2.4 years. Splines were estimated from logistic regression models. RESULTS: Lower baseline lipoprotein(a) and higher baseline insulin or HOMA-IR independently predicted 782 cases of NOD; baseline LDL-C did not predict NOD. Alirocumab reduced lipoprotein(a) and LDL-C without affecting insulin or NOD risk (odds ratio [OR] vs. placebo 0.998; 95% CI 0.860-1.158). However, in logistic regression, decreased lipoprotein(a) and LDL-C on alirocumab were independent, opposite predictors of NOD. OR for NOD for 25% and 50% lipoprotein(a) reductions on alirocumab were 1.12 (95% CI 1.01-1.23) and 1.24 (1.02-1.52). OR for NOD for 25% and 50% LDL-C reductions on alirocumab were 0.88 (95% CI 0.80-0.97) and 0.77 (0.64-0.94). CONCLUSIONS: Baseline lipoprotein(a) was inversely associated with risk of NOD. Alirocumab-induced reductions of lipoprotein(a) and LDL-C were associated with increased and decreased risk of NOD, respectively, without net effect on NOD. Ongoing trials will determine the impact of larger and longer lipoprotein(a) reductions on NOD.