  Context. It is now well-established that small, rocky planets are common
around low-mass stars. However, the detection of such planets is challenged by
the short-term activity of the host stars. Aims. The HArps-N red Dwarf
Exoplanet Survey (HADES) program is a long-term project at the Telescopio
Nazionale Galileo aimed at the monitoring of nearby, early-type, M dwarfs,
using the HARPS-N spectrograph to search for small, rocky planets. Methods. A
total of 174 HARPS-N spectroscopic observations of the M0.5V-type star GJ 9689
taken over the past seven years have been analysed. We combined these data with
photometric measurements to disentangle signals related to the stellar activity
of the star from possible Keplerian signals in the radial velocity data. We run
an MCMC analysis, applying Gaussian Process regression techniques to model the
signals present in the data. Results. We identify two periodic signals in the
radial velocity time series, with periods of 18.27 d, and 39.31 d. The analysis
of the activity indexes, photometric data, and wavelength dependency of the
signals reveals that the 39.31 d signal corresponds to the stellar rotation
period. On the other hand, the 18.27 d signal shows no relation to any activity
proxy or the first harmonic of the rotation period. We, therefore, identify it
as a genuine Keplerian signal. The best-fit model describing the newly found
planet, GJ 9689 b, corresponds to an period P$_{\rm b}$ = 18.27 $\pm$ 0.01 d,
and a minimum mass M$_{\rm P}\sin i$ = 9.65 $\pm$ 1.41 M$_{\oplus}$.
