Context : NGC 3532 is an extremely rich open cluster embedded in the Galactic disc , hitherto lacking a comprehensive , documented membership list .

Aims : We provide membership probabilities from new radial velocity observations of solar-type and low-mass stars in NGC 3532 , in part as a prelude to a subsequent study of stellar rotation in the cluster .

Methods : Using extant optical and infra-red photometry we constructed a preliminary photometric membership catalogue , consisting of 2230 dwarf and turn-off stars .
We selected 1060 of these for observation with the AAOmega spectrograph at the 3.9 m-Anglo-Australian Telescope and 391 stars for observations with the Hydra-South spectrograph at the 4 m Victor Blanco Telescope , obtaining spectroscopic observations over a decade for 145 stars .
We measured radial velocities for our targets through cross-correlation with model spectra and standard stars , and supplemented them with radial velocities for 433 additional stars from the literature .
We also measured \log g , T _ { \mathrm { eff } } , and [ Fe/H ] from the AAOmega spectra .

Results : The radial velocity distribution emerging from the observations is centred at 5.43 \pm 0.04 km s ^ { -1 } and has a width ( standard deviation ) of 1.46 km s ^ { -1 } .
Together with proper motions from Gaia DR2 we find 660 exclusive members , of which five are likely binary members .
The members are distributed across the whole cluster sequence , from giant stars to M dwarfs , making NGC 3532 one of the richest Galactic open clusters known to date , on par with the Pleiades .
From further spectroscopic analysis of 153 dwarf members we find the metallicity to be marginally sub-solar , with \mathrm { [ Fe / H ] } = -0.07 \pm 0.10 .
We confirm the extremely low reddening of the cluster , E _ { B - V } = 0.034 \pm 0.012 mag , despite its location near the Galactic plane .
Exploiting trigonometric parallax measurements from Gaia DR2 we find a distance of 484 ^ { +35 } _ { -30 } pc [ ( m - M ) _ { 0 } = 8.42 \pm 0.14 mag ] .
Based on the membership we provide an empirical cluster sequence in multiple photometric passbands .
A comparison of the photometry of the measured cluster members with several recent model isochrones enables us to confirm the 300 Myr cluster age .
However , all of the models evince departures from the cluster sequence in particular regions , especially in the lower mass range .

Conclusions :