Abstract The soft theorem states that scattering amplitude in gauge theory with a soft gauge-boson emission can be factorized into a hard scattering amplitude and a soft factor. In this paper, we present calculations of the soft factor for processes involving two hard colored partons, up to three loops in QCD. To accomplish this, we developed a systematic method for recursively calculating relevant Feynman integrals using the Feynman-Parameter representation. Our results constitute an important ingredient for the subtraction of infrared singularities at N4LO in perturbative QCD. Using the principle of leading transcendentality between QCD and N $$ \mathcal{N} $$ = 4 super Yang-Mills theory, we determine the soft factor in the latter case to three loops with full-color dependence. As a by-product, we also obtain the finite constant f 2 3 $$ {f}_2^{(3)} $$ in the Bern-Dixon-Smirnov ansatz analytically, which was previously known numerically only.
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