  We present results from VERITAS observations of the BL Lac object PG 1553+113
spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured
between 160 and 560\,GeV, is well described by a power law with a spectral
index of $4.33 \pm 0.09$. The time-averaged integral flux above $200\,$GeV
measured for this period was $(1.69 \pm 0.06) \times 10^{-11} \, \mathrm{ph} \,
\mathrm{cm}^{-2} \, \mathrm{s}^{-1}$, corresponding to 6.9\% of the Crab Nebula
flux. We also present the combined $\gamma$-ray spectrum from the Fermi Large
Area Telescope and VERITAS covering an energy range from 100~MeV to 560~GeV.
The data are well fit by a power law with an exponential cutoff at $\rm {101.9
\pm 3.2 \, \mathrm{GeV}} $. The origin of the cutoff could be intrinsic to
PG~1553+113 or be due to the $\gamma$-ray opacity of our universe through pair
production off the extragalactic background light (EBL). Given lower limits to
the redshift of $\rm z \negthinspace > \negthinspace 0.395$ based on optical/UV
observations of PG~1553+113, the cutoff would be dominated by EBL absorption.
Conversely, the small statistical uncertainties of the VERITAS energy spectrum
have allowed us to provide a robust upper limit on the redshift of PG 1553+113
of $z \negthinspace \leq \negthinspace 0.62$. A strongly-elevated mean flux of
$(2.50 \pm 0.14) \times 10^{-11} \, \mathrm{ph} \, \mathrm{cm}^{-2} \,
\mathrm{s}^{-1}$ (10.3\% of the Crab Nebula flux) was observed during 2012,
with the daily flux reaching as high as $(4.44 \pm 0.71) \times 10^{-11} \,
\mathrm{ph} \, \mathrm{cm}^{-2} \, \mathrm{s}^{-1}$ (18.3\% of the Crab Nebula
flux) on MJD 56048. The light curve measured during the 2012 observing season
is marginally inconsistent with a steady flux, giving a $\chi^2$ probability
for a steady flux of 0.03\%.
