  We study the cosmic evolution of radio sources out to $z \simeq 1.5$ using a
GMRT 610 MHz survey covering $\sim$1.86 deg$^2$ of the ELAIS N1 field with a
minimum/median rms noise 7.1/19.5\,$\mu$Jy / beam and an angular resolution of
6\,arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet
(RQ) and radio-loud (RL) Active Galactic Nuclei (AGN) using a combination of
multi-wavelength diagnostics and find evidence in support of the radio emission
in SFGs and RQ AGN arising from star formation, rather than AGN-related
processes. At high luminosities, however, both SFGs and RQ AGN display a radio
excess when comparing radio and infrared star formation rates. The vast
majority of our sample lie along the $\rm{SFR - M_{\star}}$ "main sequence" at
all redshifts when using infrared star formation rates. We derive the 610 MHz
radio luminosity function for the total AGN population, constraining its
evolution via continuous models of pure density and pure luminosity evolution
with $\rm{\Phi^{\star}\,\propto\,(\,1+\,z)^{(2.25\pm0.38)-(0.63\pm0.35)z}}$ and
$\rm{L_{610\,MHz}\,\propto\,(\,1+\,z)^{(3.45\pm0.53)-(0.55\pm0.29)z}}$
respectively. For our RQ and RL AGN, we find a fairly mild evolution with
redshift best fitted by pure luminosity evolution with
$\rm{L_{610\,MHz}\,\propto\,(\,1+\,z)^{(2.81\pm0.43)-(0.57\pm0.30)z}}$ for RQ
AGN and $\rm{L_{610\,MHz}\,\propto\,(\,1+\,z)^{(3.58\pm0.54)-(0.56\pm0.29)z}}$
for RL AGN. The 610 MHz radio AGN population thus comprises two differently
evolving populations whose radio emission is mostly SF-driven or AGN-driven
respectively.
