  We present a first lattice QCD calculation of the
transverse-momentum-dependent wave functions (TMDWFs) of the pion using
large-momentum effective theory. Numerical simulations are based on one
ensemble with 2+1+1 flavors of highly improved staggered quarks action with
lattice spacing $a=0.121$~fm from the MILC Collaboration, and one with 2 +1
flavor clover fermions and tree-level Symanzik gauge action generated by the
CLS Collaboration with $a=0.098$~fm. As a key ingredient, the soft function is
first obtained by incorporating the one-loop perturbative contributions and a
proper normalization. Based on this and the equal-time quasi-TMDWFs simulated
on the lattice, we extract the light-cone TMDWFs. The results are comparable
between the two lattice ensembles and a comparison with phenomenological
parametrization is made. Our studies provide a first attempt of $ab$ $initio$
calculation of TMDWFs which will eventually lead to crucial theory inputs for
making predictions for exclusive processes under QCD factorization.
