We report the discovery of a galaxy cluster at z=1.27. ClG J0848+4453 was found in a near{endash}IR field survey as a high density region of objects with very red J{minus}K colors. Optical spectroscopy of a limited number of 24{approx_lt}R{approx_lt}25 objects in the area shows that 6 galaxies within a 90 arcsec (0.49h{sub 100}{sup {minus}1} Mpc, q{sub 0}=0.1) diameter region lie at z=1.273{plus_minus}0.002. Most of these 6 member galaxies have broad-band colors consistent with the expected spectral energy distribution of a passively-evolving elliptical galaxy formed at high redshift. An additional 2 galaxies located {approximately}2 arcmin from the cluster center are also at z=1.27. Using all 8 of these spectroscopic members, we estimate the velocity dispersion {sigma}=700{plus_minus}180 km s{sup {minus}1}, which is similar to that of Abell richness class R=1 clusters in the present epoch. A deep {ital ROSAT}/PSPC observation detects X-ray emission at the 4.5{sigma} level coincident with the nominal cluster center. Assuming that the X-ray flux is emitted by hot gas trapped in the potential well of a collapsed system (no AGN are known to exist in the area), the resulting X-ray luminosity in the rest frame 0.1{endash}2.4 keV band of L{sub x}=1.5{times}10{sup 44} ergs s{sup {minus}1} suggests the presencemore » of a moderately massive system. ClG J0848+4453 is the highest redshift cluster found in a field survey. {copyright} {ital 1997 American Astronomical Society.}« less