Signalling activity of the Notch receptor, which plays a fundamental role in metazoan cell fate determination, is controlled at multiple levels. We uncovered a Notch signal-controlling mechanism that depends on the ability of the non-visual β-arrestin, Kurtz (Krz), to influence the degradation and, consequently, the function of the Notch receptor. We identified Krz as a binding partner of a known Notch-pathway modulator, Deltex (Dx), and demonstrated the existence of a trimeric Notch–Dx–Krz protein complex. This complex mediates the degradation of the Notch receptor through a ubiquitination-dependent pathway. Our results establish a novel mode of regulation of Notch signalling and define a new function for non-visual β-arrestins.