Styx was discovered by a team led by astronomer Mark R. Showalter, using fourteen sets of images taken between 26 June and 9 July 2012 by the Wide Field Camera 3 fitted to the Hubble.

[11][13][14] The survey work leading to the discovery of Styx was in preparation for the mission of the uncrewed New Horizons spacecraft, which flew by the Pluto system on 14 July 2015.

[16] However, the New Horizons spacecraft did not detect any smaller moons or rings and it passed through the Pluto system safely.

[18][19] These figures were inferred from the apparent magnitude of Styx and by using an estimated albedo of 0.35 and 0.04 for the lower and upper bounds, respectively.

[5] It is thought to have formed from the debris lofted by a collision, which would have led to losses of the more volatile ices, such as those of nitrogen and methane, in the composition of the impactors.

All of Pluto's moons appear to travel in orbits that are very nearly circular and coplanar, described by Styx's discoverer Mark Showalter as "neatly nested ... a bit like Russian dolls".

With the other moons Nix, Kerberos, and Hydra, it forms part of an unusual 1:3:4:5:6 (period ratio) sequence of near resonances.

[24][25] The 'Romulus' suggestion was discounted, as there is already an asteroid moon of that name,[26] but Vulcan won the poll after Shatner tweeted about it, with Cerberus (the dog that guards Pluto's underworld) coming second and Styx (the goddess of the river of the same name in the underworld) coming third.