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Abstract Cellular membranes provide a unique platform for interactions that drive emergent behaviors in protein dynamics and cellular signaling, distinct from those observed in solution. We investigated the proline‐rich region (PRR) and Src Homology 3 (SH3) domains of Bruton's tyrosine kinase (Btk) and its phase separation driven by the weak interactions of regulatory domains at membrane surfaces. Using supported lipid bilayers (SLBs) and giant unilamellar vesicles (GUVs), we demonstrate that membrane localization amplifies weak PRR‐SH3 interactions, enabling the formation of higher‐order assemblies and phase‐separated condensates. These assemblies, previously undescribed by solution‐state studies, are supported by reductions in the lateral diffusion of membrane‐bound Btk molecules and the stabilization of reversible condensates at the membrane surface. Constructs containing the native PRR and SH3 domains reliably formed membrane‐associated clusters, while mutation or deletion of these domains lessened changes in diffusion and impaired condensate formation. Our findings establish the membrane as an essential mediator of PRR‐SH3‐driven phase separation in Btk, thereby advancing our understanding of membrane‐specific regulation in signaling protein dynamics.