Insight into the conformational dynamics of proteins is essential towards understanding their function at a molecular level. The motions experienced by individual atoms in the protein can be precisely quantified through NMR relaxation rates, but their measurement requires well-resolved spectral responses. Two-dimensional 1H‑15N correlation spectra are the standard approach to resolve amide signals in protein NMR, but come with an excessive cost in experimental time when spectra are heavily congested due to limited 15N chemical shift dispersions. This limitation often thwarts complete characterization of dynamics for intrinsically disordered proteins, especially when they feature low-complexity or homopolymer amino acid sequences. Here, we introduce an ultra-selective 1H-15N NMR method that allows high-quality measurement of individual 15N spin-relaxation constants using fast 1D NMR spectra, even when 15N resonances are merely 6-8 Hz apart. We demonstrate the new experiment by characterizing, for the first time, pico- to nanosecond dynamics along a 16‑residue polyglutamine stretch within the protein huntingtin, the causal agent of Huntington’s disease, as well as millisecond conformational exchange in the SH3GL3 protein. The new experiment will find wide application in the study of conformational dynamics of intrinsically disordered proteins or any other biomacromolecule that features highly dense 1H-15N 2D spectra. This deposit contains Bruker pulse sequences of the SNIPER 15N R1, SNIPER 15N R1rho, SNIPER 1H-15N nOe and SNIPER zz-exchange experiments, pulse shapes used, and the NMR experimental data (Bruker format). See the Data_overview.pdf file for a more detailed description. Version 2 : Additional data has been added concerning part 3 of the Supplementary Information.