Heparin‐induced thrombocytopenia (HIT) is an adverse reaction characterized by anti‐PF4‐heparin antibody generation and hypercoagulability. Imaging flow cytometry (IFC) provides a detailed morphological analysis of platelets, which change upon activation. We evaluated IFC‐derived morphometric features to detect platelet activation and developed a functional assay for HIT diagnosis. We analysed blood samples from 42 patients with suspected HIT and extracted platelet size, shape and texture features using IFC. The morphological features were compared with CD62P expression, light transmission aggregometry (LTA) and a serotonin release assay (SRA) in terms of their ability to predict a HIT diagnosis. Five IFC‐derived morphological features (area, circularity, contrast, diameter and major axis) significantly distinguished resting from activated platelets. The major axis feature performed best for HIT diagnosis, with a sensitivity of 89.3% and a specificity of 92.9% versus functional assays (LTA/SRA); this diagnostic performance was similar to that of CD62P expression on the same platelet donors. The area and diameter had similar specificity (92.9%) and a slightly lower sensitivity (85.7%). The morphological features associated with platelet activation might be effective markers for the diagnosis of HIT, matching platelet CD62P expression assay performance. The high‐throughput IFC exploration of platelet activation offers new perspectives in label‐free analysis and time‐saving.