Electrical transport with temperature-induced spin disorder in NiMnSb

•Finite-temperature electron transport is studied by ab initio alloy analogy model.•Phonons, magnons and chemical disorder are treated in a unified way.•Calculations reproduce successfully the measured electrical resistivity.•At temperature 600 K, spin polarization of the current as high as 80% is predicted.•At the Curie temperature 730 K, the Matthiessen’s rule is violated by 16%.