We present a measurement of the cosmic microwave background (CMB) gravitational lensing potential using data from the first two seasons of observations with SPTpol, the polarization-sensitive receiver currently installed on the South Pole Telescope (SPT). The observations used in this work cover 100 deg$^2$ of sky with arcminute resolution at 150 GHz. Using a quadratic estimator, we make maps of the CMB lensing potential from combinations of CMB temperature and polarization maps. We combine these lensing potential maps to form a minimum-variance (MV) map. The lensing potential is measured with a signal-to-noise ratio of greater than one for angular multipoles between $100< L <250$. This is the highest signal-to-noise mass map made from the CMB to date and will be powerful in cross-correlation with other tracers of large-scale structure. We calculate the power spectrum of the lensing potential for each estimator, and we report the value of the MV power spectrum between $100< L <2000$ as our primary result. We constrain the ratio of the spectrum to a fiducial $Lambda$CDM model to be $A_{rm MV}=0.92 pm 0.14 {rm, (Stat.)} pm 0.08 {rm, (Sys.)}$. Restricting ourselves to polarized data only, we find $A_{rm POL}=0.92 pm 0.24 {rm, (Stat.)} pm 0.11 {rm, (Sys.)}$. This measurement rejects the hypothesis of no lensing at $5.9 sigma$ using polarization data alone, and at $14 sigma$ using both temperature and polarization data.
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