  We present the serendipitous discovery of a late T-type brown dwarf candidate
in JWST NIRCam observations of the Early Release Science Abell 2744 parallel
field. The discovery was enabled by the sensitivity of JWST at 4~$\mu$m
wavelengths and the panchromatic 0.9--4.5~$\mu$m coverage of the spectral
energy distribution. The unresolved point source has magnitudes F115W =
27.95$\pm$0.15 and F444W = 25.84$\pm$0.01 (AB), and its F115W$-$F444W and
F356W$-$F444W colors match those expected for other, known T dwarfs. We can
exclude it as a reddened background star, high redshift quasar, or very high
redshift galaxy. Comparison with stellar atmospheric models indicates a
temperature of $T_{eff}$ $\approx$ 600~K and surface gravity $\log{g}$
$\approx$ 5, implying a mass of 0.03~M$_{\odot}$ and age of 5~Gyr. We estimate
the distance of this candidate to be 570--720~pc in a direction perpendicular
to the Galactic plane, making it a likely thick disk or halo brown dwarf. These
observations underscore the power of JWST to probe the very low-mass end of the
substellar mass function in the Galactic thick disk and halo.
