Larissa was first discovered by Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David J. Tholen, based on fortuitous ground-based stellar occultation observations[14] on May 24, 1981.

[15] The moon was later recovered and confirmed to be the only object in its orbit during the Voyager 2 flyby in 1989[16] after which it received the additional designation S/1989 N 2 on August 2, 1989.

[19] Larissa's orbit is nearly circular and lies below Neptune's synchronous orbit radius, which means it is slowly spiralling inward due to tidal deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching, similarly to how Triton will eventually collide with Neptune or break into a planetary ring.

Compositionally, Larissa appears to be similar to other small inner Neptunian satellites, with a deep 3.0 micron feature attributed to water ice or hydrated silicate minerals.

[21] The probe was able to get some photographs with details of Larissa, showing its cratered surface; unlike the other inner moons of Neptune that only appeared as dots or smudges.