We present the first result on the three-loop parton (quark/gluon) jet function in perturbative quantum chromodynamics using already known three-loop coefficient functions for deep-inelastic scattering via the exchange of a virtual photon that couples to quarks or a scalar that couples to gluons. While the gluon jet function is a brand new result emerging from this article, the result for the quark jet function provides an independent check to a more recent calculation. These jet functions being universal ingredients in the Soft-collinear effective theory framework, will play an important role in the phenomenological studies at the Large Hadron Collider, such as resummation of jet observables and also in N-jettiness subtraction method.