  We report the discovery and characterization of the transiting extrasolar
planet TOI-1710$\:$b. It was first identified as a promising candidate by the
Transiting Exoplanet Survey Satellite (TESS). Its planetary nature was then
established with SOPHIE and HARPS-N spectroscopic observations via the
radial-velocity method. The stellar parameters for the host star are derived
from the spectra and a joint Markov chain Monte-Carlo (MCMC) adjustment of the
spectral energy distribution and evolutionary tracks of TOI-1710. A joint MCMC
analysis of the TESS light curve and the radial-velocity evolution allows us to
determine the planetary system properties. From our analysis, TOI-1710$\:$b is
found to be a massive warm super-Neptune ($M_{\rm p}=28.3\:\pm\:4.7\:{\rm
M}_{\rm Earth}$ and $R_{\rm p}=5.34\:\pm\:0.11\:{\rm R}_{\rm Earth}$) orbiting
a G5V dwarf star ($T_{\rm eff}=5665\pm~55\mathrm{K}$) on a nearly circular
24.3-day orbit ($e=0.16\:\pm\:0.08$). The orbital period of this planet is
close to the estimated rotation period of its host star $P_{\rm
rot}=22.5\pm2.0~\mathrm{days}$ and it has a low Keplerian semi-amplitude
$K=6.4\pm1.0~\mathrm{m\:s^{-1}}$; we thus performed additional analyses to show
the robustness of the retrieved planetary parameters. With a low bulk density
of $1.03\pm0.23~\mathrm{g\:cm^{-3}}$ and orbiting a bright host star ($J=8.3$,
$V=9.6$), TOI-1710$\:$b is one of the best targets in this mass-radius range
(near the Neptunian desert) for atmospheric characterization via transmission
spectroscopy, a key measurement in constraining planet formation and
evolutionary models of sub-Jovian planets.
