The dynamics of isolated-photon plus jet production in $pp$ collisions at $\sqrt{s}$ = 13 TeV were studied with the ATLAS detector at the LHC, using a dataset with an integrated luminosity of 3.2 fb$^{-1}$. The photons were reconstructed for photon transverse energies larger than 125 GeV. The jets were identified using the anti-$k_{t}$ algorithm with radius parameter R=0.4 and selected in the rapidity range $|y| <$ 2.37, for transverse momenta $p_\mathrm{T} >$ 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the photon transverse energy, the jet transverse momentum, the azimuthal separation between the selected photon and the jet, the photon-jet invariant mass and the scattering angle in the photon-jet centre-of-mass system. The leading-logarithm parton-shower preditions from SHERPA and PYTHIA as well as the next-to-leading order QCD calculations from JETPHOX and multi-leg plus parton shower NLO SHERPA are compared to the measurements.