  We present a comprehensive study of the massive binary system HM1~8, based on
multi-epoch high resolution spectroscopy, $V$-band photometry and archival
X-ray data. Spectra from the OWN Survey, a high resolution optical monitoring
of Southern O and WN stars, are used to analyse the spectral morphology and
perform quantitative spectroscopic analysis of both stellar components. The
primary and secondary components are classified as O4.5~IV(f) and O9.7~V,
respectively. From a radial-velocity (RV) study we derived a set of orbital
parameters for the system. We found an eccentric orbit ($e=0.14 \pm 0.01$) with
a period of $P = 5.87820 \pm 0.00008$~days. Through the simultaneous analysis
of the RVs and the $V$-band light curve we derived an orbital inclination of
$70.0^{\circ} \pm 2.0$ and stellar masses of
$M_a=33.6^{+1.4}_{-1.2}~\text{M}_{\sun}$ for the primary, and
$M_b=17.7^{+0.5}_{-0.7}~\text{M}_{\sun}$ for the secondary. The components show
projected rotational velocities $v_1\sin{i}=105 \pm 14~\text{km~s}^{-1}$ and
$v_2\sin{i}=82 \pm 15~\text{km~s}^{-1}$, respectively. A tidal evolution
analysis is also performed and found to be in agreement with the orbital
characteristics. Finally, the available X-ray observations show no evidence of
a colliding winds region, therefore the X-ray emission is attributed to stellar
winds.
