  We report the $\gamma$-ray detection of a young radio galaxy, PKS 1718$-$649,
belonging to the class of Compact Symmetric Objects (CSOs), with the Large Area
Telescope (LAT) on board the {\it Fermi} satellite. The third {\it Fermi}
Gamma-ray LAT catalog (3FGL) includes an unassociated $\gamma$-ray source, 3FGL
J1728.0$-$6446, located close to PKS 1718$-$649. Using the latest Pass 8
calibration, we confirm that the best fit $1 \sigma$ position of the
$\gamma$-ray source is compatible with the radio location of PKS 1718$-$649.
Cross-matching of the $\gamma$-ray source position with the positions of blazar
sources from several catalogs yields negative results. Thus, we conclude that
PKS 1718$-$649 is the most likely counterpart to the unassociated LAT source.
We obtain a detection test statistics TS$\sim 36$ ($>$5$\sigma$) with a best
fit photon spectral index $\Gamma=$2.9$\pm$0.3 and a 0.1-100 GeV photon flux
density $F_{\rm 0.1-100GeV}=$(11.5$\pm$0.3)$\times{\rm 10^{-9}}$ ph cm$^{-2}$
s$^{-1}$. We argue that the linear size ($\sim$2 pc), the kinematic age
($\sim$100 years), and the source distance ($z=0.014$) make PKS 1718$-$649 an
ideal candidate for $\gamma$-ray detection in the framework of the model
proposing that the most compact and the youngest CSOs can efficiently produce
GeV radiation via inverse-Compton scattering of the ambient photon fields by
the radio lobe non-thermal electrons. Thus, our detection of the source in
$\gamma$-rays establishes young radio galaxies as a distinct class of
extragalactic high-energy emitters, and yields an unique insight on the
physical conditions in compact radio lobes interacting with the interstellar
medium of the host galaxy.
