The present disclosure provides a large combinatorial library of cell-permeable bicyclic peptides. The bicyclic peptides described herein include the first ring consisted of randomized peptide sequences for potential binding to a target of interest while the second ring featured a family of different cell-penetrating motifs, for both cell penetration and target binding. The library was screened against the IκB kinase α/β (IKKα/β)-binding domain of NF-κB essential modulator (NEMO), resulting in the discovery of several cell-permeable bicyclic peptides which inhibited the NEMO-IKKβ interaction, thereby selectively inhibiting canonical NF-κB signaling in mammalian cells and the proliferation of cisplatin-resistant ovarian cancer cells.