Brassinosteroids (BRs) are plant steroid hormones that control many aspects of plant growth and development. BRs are perceived at the cell-surface by the plasma membrane-localized receptor complex composed of the receptor kinase BRI1 and its co-receptor BAK1. Here we show that BRI1 is post-translationally modified by K63 polyubiquitin chains in vivo. Artificially ubiquitinated BRI1 is recognized at the trans-Golgi Network/Early Endosomes (TGN/EE) and rapidly routed for vacuolar degradation. Mass spectrometry analyses identified residue K866 as an in vivo ubiquitination target in BRI1 involved in the negative regulation of BRI1. Model prediction revealed several redundant ubiquitination sites required for the endosomal sorting and vacuolar targeting of BRI1. Using total internal reflection fluorescence microscopy (TIRF), we also uncovered a role for BRI1 ubiquitination in promoting internalization from the cell-surface. Finally, we demonstrate that the control of BRI1 protein dynamics by ubiquitination is a fundamental control mechanism for BR responses in plants. Altogether, our results identify K63-linked polyubiquitin chain formation as a dual targeting signal for BRI1 internalization and sorting along the endocytic pathway, and highlight its role in hormonally controlled plant development.