  Source classifications, stellar masses and star formation rates are presented
for 80,000 radio sources from the first data release of the Low Frequency Array
Two-metre Sky Survey (LoTSS) Deep Fields, which represents the widest deep
radio survey ever undertaken. Using deep multi-wavelength data spanning from
the ultraviolet to the far-infrared, spectral energy distribution (SED) fitting
is carried out for all of the LoTSS-Deep host galaxies using four different SED
codes, two of which include modelling of the contributions from an active
galactic nucleus (AGN). Comparing the results of the four codes, galaxies that
host a radiative AGN are identified, and an optimised consensus estimate of the
stellar mass and star-formation rate for each galaxy is derived. Those galaxies
with an excess of radio emission over that expected from star formation are
then identified, and the LoTSS-Deep sources are divided into four classes:
star-forming galaxies, radio-quiet AGN, and radio-loud high-excitation and
low-excitation AGN. Ninety-five per cent of the sources can be reliably
classified, of which more than two-thirds are star-forming galaxies, ranging
from normal galaxies in the nearby Universe to highly-starbursting systems at
z>4. Star-forming galaxies become the dominant population below 150-MHz flux
densities of about 1 mJy, accounting for 90 per cent of sources at a 150-MHz
flux density of 100 microJy. Radio-quiet AGN comprise around 10 per cent of the
overall population. Results are compared against the predictions of the SKADS
and T-RECS radio sky simulations, and improvements to the simulations are
suggested.
