  We present the first calculation of the $x$-dependence of the proton
generalized parton distributions (GPDs) within lattice QCD. Results are
obtained for the isovector unpolarized and helicity GPDs. We compute the
appropriate matrix elements of fast-moving protons coupled to non-local
operators containing a Wilson line. We present results for proton momenta
$0.83,\,1.25,\,1.67$ GeV, and momentum transfer squared $0.69,\,1.38$ GeV$^2$.
These combinations include cases with zero and nonzero skewness. The
calculation is performed using one ensemble of two degenerate mass light, a
strange and a charm quark of maximally twisted mass fermions with a clover
term. The lattice results are matched to the light-cone GPDs using one-loop
perturbation theory within the framework of large momentum effective theory.
The final GPDs are given in the $\overline{\rm MS}$ scheme at a scale of 2 GeV.
