Growing up in the municipality of Rennebu in Norway, Smeplass got into music at an early age.
At age of 9 she submitted to participate on MGPjr. with ten year old Celine Helgemo under the artist name AC: The Blue Snoopies. The duo was not selected to participate in the music competition, but Celine later won Melodi Grand Prix Junior 2007 with the song "Bæstevænna" which was about Astrid.
At the age of 16 she participated in the Norwegian version of Pop Idol in 2013, and at that time released a single, "Shattered", under the name Astrid Smeplass. The song was cowritten by American singer-songwriter Melanie Fontana. Astrid released her first single "2AM" under her new artist image at the age of 18 on Universal Music. "2AM" was released in the US in 2015. She also released a cover-version of the single "FourFiveSeconds".
At the age of 17, she quit high school to focus on her musical career.
In 2016, Smeplass supported Troye Sivan on his European tour, and she released a self-titled EP on 20 May 2016.
In 2017, Smeplass provided backing vocals on "Hey Hey Hey" by American singer Katy Perry from her album Witness.
Anna S represented her home country Norway in the 2nd Edition of the Love Wave Contest with her Song "Hurts so Good" She will perform in the 2nd Semi Final.