A new method for brightening wool during dyeing has been developed using tert-butylamine borane in the dyebath. The method was found to be significantly superior to current industrial practice using hydroxylammonium sulphate or its derivatives. The effects of tert-butylamine borane on dye shades and dyeing quality have also been assessed with a range of commercial wool dyes. The results of this study have shown that the new method is effective in preventing hydrothermal wool yellowing during dyeing, and can produce brighter shades of dyeings without significantly altering the dye shades or impairing the dyeing fastness and mechanical properties of the dyed wool under the conditions examined. The advantages of the concurrent bleaching and dyeing method over conventional bleaching and dyeing processes include reduced processing time, improved energy efficiency, and lower water consumption, arising from reduction in the number of fiber treatment steps.