  We report a comprehensive study on the electronic transport properties of
SrZn$_2$Ge$_2$ single crystals. The in-plane electrical resistivity of the
compound exhibits linear temperature dependence for 80 K < T < 300 K, and T^2
dependence below 40 K, consistent with the Fermi liquid behavior. Both the
transverse and longitudinal magnetoresistance exhibit a crossover at critical
field B* from weak-field quadratic-like to high-field unsaturated linear field
dependence at low temperatures (T \leq 50 K). Possible sources of linear
magnetoresistance are discussed based on the Fermi surface topology, classical
and quantum transport models. The Hall resistivity data establish
SrZn$_2$Ge$_2$ as a multiband system with contributions from both the electrons
and holes. The Hall coefficient is observed to decrease with increasing
temperature and magnetic field, changing its sign from positive to negative.
The negative Hall coefficient observed at low temperatures in high fields and
at high temperatures over the entire field range suggests that the highly
mobile electron charge carriers dominate the electronic transport. Our
first-principles calculations show that nontrivial topological surface states
exist in SrZn$_2$Ge$_2$ within the bulk gap along the {\Gamma}-M path. Notably,
these surface states extend from the valence to conduction band with their
number varying based on the Sr and Ge termination plane. The Fermi surface of
the compound exhibits a distinct tetragonal petal-like structure, with one open
and several closed surfaces. Overall, these findings offer crucial insights
into the mechanisms underlying the electronic transport of the compound.
