Agneson was born and raised in the small town of Eskilstuna, Sweden. She began acting, singing, and dancing as a child in minor stage productions. She moved to London at age fifteen to pursue her career. She has also been in Little Kingdom, The Courier, and Clark.
- Agneson revealed on Sverigesradio that the strangling scene in Season 5 Episode 20, Ragnarok, wasn't simulated. She wanted the scene to look as realistic as possible and was taken care of by a paramedic on set and co-star Alex Høgh Andersen (Ivar) despite originally being advised against it by the crew due to the risks.