Relaxor ferroelectrics exhibit outstanding dielectric, electromechanical and electrocaloric properties, and are the materials of choice for acoustic sensors, solid-state coolers, transducers and actuators(1-4). Despite more than five decades of intensive study, relaxor ferroelectrics remain one of the least understood material families in ferroelectric materials and condensed matter physics(5-14). Here, by combining X-ray diffraction, atomic force microscope infrared spectroscopy and first-principles calculations, we reveal that the relaxor behaviour of ferroelectric polymers originates from conformational disorder, completely different from classic perovskite relaxors, which are typically characterized by chemical disorder. We show that chain chirality is essential to the formation of the disordered helix conformation arising from local distortions ofgauchetorsional angles, which consequently give rise to relaxor properties in polymers. This study not only sheds light on the fundamental mechanisms of relaxor ferroelectrics, but also offers guidance for the discovery of new ferroelectric relaxor organic materials for flexible, scalable and biocompatible sensor and energy applications. Relaxor ferroelectric polymers are a material of choice for applications such as electrostrictive actuators or electrocaloric cooling. Here, the origin of relaxor behaviour at the molecular level is investigated and found to arise from conformational disorder.