Atherosclerosis is a primary global health concern due to its high morbidity and mortality. This disease is characterized by a complex interplay of chronic inflammation, oxidative stress, and proteolytic enzymes. Traditional imaging techniques struggle to capture the dynamic biochemical processes within atherosclerotic plaques. Herein, we have developed a novel unimolecular photoacoustic probe (UMAPP) that combines specific recognition sites for neutrophil elastase (NE) and the redox pair O2•‒/GSH into a cohesive molecular platform, allowing in vivo monitoring of oxidative stress and activated neutrophils within plaques. UMAPP features a boron-dipyrromethene (BODIPY) core linked to a hydrophilic NE-cleavable tetrapeptide, and dual oxidative stress-responsive catechol moieties, enabling NE-mediated modulation of photoinduced electron transfer, affecting the photoacoustic intensity at 685 nm (PA685), while oxidation and reduction of the catechol groups by O2•‒ and GSH lead to reversible, ratiometric changes in the photoacoustic spectrum. Preliminary applications of UMAPP have successfully differentiated between atherosclerotic and healthy mice, assessed the impact of pneumonia on plaque composition, and validated the probe's efficacy in drug-treatment studies, detecting molecular changes prior to observable histopathological alterations. UMAPP's integrated molecular imaging approach holds significant promise for advancing the diagnosis and management of atherosclerosis by enabling earlier and more precise detection of vulnerable plaques.