Peptide ligation chemistry has revolutionized protein science by providing access to homogeneously modified peptides and proteins. However, lipidated polypeptides and integral membrane proteins-an important class of biomolecules-remain enormously challenging to access synthetically owing to poor aqueous solubility of one or more of the fragments under typical ligation conditions. Herein we describe the advent of a reductive diselenide-selenoester ligation (rDSL) method that enables efficient ligation of peptide fragments down to low nanomolar concentrations, without resorting to solubility tags or hybridizing templates. The power of rDSL is highlighted in the efficient synthesis of the FDA-approved therapeutic lipopeptide tesamorelin and palmitylated variants of the transmembrane lipoprotein phospholemman (FXYD1). Lipidation of FXYD1 was shown to critically modulate inhibitory activity against the Na+/K+ pump.