Optical microplate-based biosensors combine the advantages of label-free detection with industry-standard assay laboratory infrastructure and scalability. A plate-based label-free platform allows the same basic platform to be used to quantify molecular interactions of macromolecules and to screen and characterize drug-like small-molecule interactions. The ligand-binding domain of orphan estrogen-related nuclear receptor-γ (ERRγ) is utilized, as a model system of a challenging type of target, to illustrate the rapid development and utility of a range of biochemical assay formats on these biosensors. Formats in which either the domain, or a peptide derived from its cognate corepressor, RIP140, were immobilized were utilized. The direct binding of small drug molecules to the domain was characterized using immobilized domain. Subsequent addition of peptide distinguished whether compounds acted as either antagonists of peptide binding, or as agonists promoting a ternary complex. The format with peptide immobilized gave a more sensitive procedure for establishing the effect of compounds on the domain-peptide interaction. Using a direct-binding format, a diverse chemical library of 1,408 compounds in DMSO was screened for ability to bind to biosensors coated with ERRγ ligand-binding domain. Hits were then characterized using the other biosensor assay formats. The standard requirements for a full primary screening campaign were fulfilled by the acceptable hit-rate, quality-performance parameters, and throughput of the direct-binding assay format. Such a format allows direct screening of targets, such as orphan receptors, without the requirement for prior knowledge of a validated ligand.