  Using the Murchison Widefield Array (MWA), the low-frequency Square Kilometre
Array (SKA1 LOW) precursor located in Western Australia, we have completed the
GaLactic and Extragalactic All-sky MWA (GLEAM) survey, and present the
resulting extragalactic catalogue, utilising the first year of observations.
The catalogue covers 24,831 square degrees, over declinations south of
$+30^\circ$ and Galactic latitudes outside $10^\circ$ of the Galactic plane,
excluding some areas such as the Magellanic Clouds. It contains 307,455 radio
sources with 20 separate flux density measurements across 72--231MHz, selected
from a time- and frequency- integrated image centred at 200MHz, with a
resolution of $\approx 2$'. Over the catalogued region, we estimate that the
catalogue is 90% complete at 170mJy, and 50% complete at 55mJy, and large areas
are complete at even lower flux density levels. Its reliability is 99.97% above
the detection threshold of $5\sigma$, which itself is typically 50mJy. These
observations constitute the widest fractional bandwidth and largest sky area
survey at radio frequencies to date, and calibrate the low frequency flux
density scale of the southern sky to better than 10%. This paper presents
details of the flagging, imaging, mosaicking, and source
extraction/characterisation, as well as estimates of the completeness and
reliability. All source measurements and images are available online
(http://www.mwatelescope.org/science/gleam-survey). This is the first in a
series of publications describing the GLEAM survey results.
