This double-blind, parallel, two-arm study will evaluate the potential to reduce cardiovascular risk, the tolerability and long-term safety profile of aleglitazar compared to placebo on top of standard care in patients with recent acute coronary syndrome (ACS) and type 2 diabetes mellitus. Patients will be randomized to receive either aleglitazar or placebo once daily as oral doses. The study will last until at least 950 events occur, but time on study treatment will be for at least 2.5 years.