Lanthanides (Ln3+) provide attractive physicochemical, magnetic and optical properties, triggering the development of lanthanide-binding peptides for structural biology1,2 and bioimaging3, as well as artificial metalloenzymes for photoredox catalysis4. However, their strong oxophilicity evokes the tendency for unspecific binding on protein surfaces and sequestration, which often requires multiple rounds of scaffold optimization to obtain strong and site-specific Ln3+ binding. An efficient screening method, as reported for short synthetic peptides by Imperiali and co-workers 5, is not yet available for proteins. We thus developed a plate-based screening platform to identify novel lanthanide-binding proteins by combining purification and on-resin Ln3+ loading on commercial filter plates with a dual luminescence readout employing internal and external sensitizers. The stringency of this protocol enabled the screening of metal-binding peptides fused to a large expression tag, which we used for proof of concept. Furthermore, we designed a smart library based on de novo helical bundle scaffolds with introduced aspartate/glutamate residues for dative Ln3+ binding and screened them with our procedure. We could identify new lanthanide-binding proteins with binding affinities in the µM to nM range, distinct metal specificity and increased thermostability in response to Ln3+ binding. In conclusion, the established plate-based screening platform allows the detection of Ln3+ binding peptides and proteins and thus complements the currently available methods.