Measurements of the dark energy equation-of-state parameter , w , have been limited by uncertainty in the selection effects and photometric calibration of z < 0.1 Type Ia supernovae ( SNe Ia ) . The Foundation Supernova Survey is designed to lower these uncertainties by creating a new sample of z < 0.1 SNe Ia observed on the Pan-STARRS system . Here , we combine the Foundation sample with SNe from the Pan-STARRS Medium Deep Survey and measure cosmological parameters with 1,338 SNe from a single telescope and a single , well-calibrated photometric system . For the first time , both the low- z and high- z data are predominantly discovered by surveys that do not target pre-selected galaxies , reducing selection bias uncertainties . The z > 0.1 data include 875 SNe without spectroscopic classifications and we show that we can robustly marginalize over CC SN contamination . We measure Foundation Hubble residuals to be fainter than the pre-existing low- z Hubble residuals by 0.046 \pm 0.027 mag ( stat+sys ) . By combining the SN Ia data with cosmic microwave background constraints , we find w = -0.938 \pm 0.053 , consistent with \Lambda CDM . With 463 spectroscopically classified SNe Ia alone , we measure w = -0.933 \pm 0.061 . Using the more homogeneous and better-characterized Foundation sample gives a 55 % reduction in the systematic uncertainty attributed to SN Ia sample selection biases . Although use of just a single photometric system at low and high redshift increases the impact of photometric calibration uncertainties in this analysis , previous low- z samples may have correlated calibration uncertainties that were neglected in past studies . The full Foundation sample will observe up to 800 SNe to anchor the LSST and WFIRST Hubble diagrams .