We report the discovery of TOI-3493 b, a sub-Neptune-sized planet on an 8.15-d orbit transiting the bright (V=9.3) G0 star HD 119355 (aka TIC 203377303) initially identified by NASA's TESS space mission. With the aim of confirming the planetary nature of the transit signal detected by TESS and determining the mass of the planet, we performed an intensive Doppler campaign with the HARPS spectrograph, collecting radial velocity measurements. We found that TOI-3493 b lies in a nearly circular orbit and has a mass of 9.0 ± 1.2 M⊕ and a radius of 3.22 ± 0.08 R⊕, implying a bulk density of 1.47-0.22+0.23 g cm‑3, consistent with a composition comprising a small solid core surrounded by a thick H/He-dominated atmosphere.