Its discovery was announced by Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden on 4 May 2005 from observations taken between 12 December 2004, and 11 March 2005.

It had the largest semi-major axis among all the known moons of Saturn[3] It is about 6 kilometres in diameter, and it orbits Saturn at an average distance of 23,609 Mm in 1491 d at an inclination of 168° to the ecliptic (160° to Saturn's equator) in a retrograde direction and with an eccentricity of 0.186.

It is ambiguous whether the rotation period is 6.9 or 9.5±0.4 hours, but it is known to show very little variation in brightness and is probably very round in shape.

It was also the faintest moon that was measured by Cassini–Huygens.

[2][3] Fornjot was named after Fornjót, a giant in Norse mythology.