In cancer, proliferation of malignant cells is driven by overactivation of growth-signalling mechanisms, such as the epidermal growth factor receptor (EGFR) pathway. Despite its therapeutic relevance, the EGF-EGFR interaction has remained elusive to inhibition by synthetic molecules, mostly as a result of its large size and lack of binding pockets and cavities. Designed peptides, featuring cyclic motifs and other structural constraints, have the potential to modulate such challenging protein-protein interactions (PPIs). Herein, we present the structure-based design of a series of bicyclic constrained peptides that mimic an interface domain of EGFR and inhibit the EGF-EGFR interaction by targeting the smaller partner (i.e., EGF). This design process was guided by the integrated use of in silico methods and biophysical techniques, such as NMR spectroscopy and surface acoustic wave. The best analogues were able to reduce selectively the viability of EGFR+ human cancer cells. In addition to their efficacy, these bicyclic peptides are endowed with exceptional stability and metabolic resistance-two features that make them suitable candidates for in vivo applications.