Thyroid hormone receptors (TRs) are members of the nuclear hormone receptor superfamily and regulate many homeostatic processes, including basal metabolism, cardiovascular function, body weight, and lipid trafficking. Upon binding of the ligand triiodothyronine (T3), TR undergoes a conformational change that releases corepressors and recruits coactivators, such as Steroid Receptor Coactivator 2 (SRC2); in turn, these modulate the expression of target genes. In this report, we used a TRβ-SRC2 fluorescence polarization assay to screen the Molecular Libraries Small Molecule Repository (MLSMR) and identify a novel methylsulfonylnitrobenzoate (MSNB)-containing series that blocks the association of TRβ with a SRC2 peptide. This inhibitor probe molecule, ML151 (CID 5184800), blocked TRβ-SRC2 interaction with a potency of 1.8μM. Mechanistic studies revealed that ML151 (CID 5184800) is a covalent inhibitor and binds irreversibly to Cys298 within the AF-2 cleft of TRβ. This series will be useful for in vitro mechanistic studies of TR-SRC2 interactions, as well as other nuclear hormone receptor-coactivator interactions.