Knardahl made her concert debut at age 12 with the Oslo Philharmonic, performing concertos by Bach, Haydn and Weber on a single program, according to the Music Information Centre Norway (MIC).
In the wake of World War II, Knardahl left Europe in 1946 to spend two decades in the US, according to Aftenposten, and was the resident pianist with the Minneapolis Symphony (now the Minnesota Orchestra) for 15 seasons.
In 1967 she returned to her homeland and "swept into Norwegian musical circles like a fresh breeze," according to Aftenposten music critic Idar Karevold. She became popular not only with concert audiences but also as a television performer, thanks to her warm personality and sense of humor.
Knardahl made a number of recordings, most notably a 10-volume set of the complete piano music of Edvard Grieg on the BIS label. In addition, she was a highly regarded teacher and served as the first Professor of Chamber Music in the history of the Norwegian State Academy of Music.
In 1968 Knardahl won the top prize from the Norwegian music critics' national association and in 1980 was awarded the Grieg Prize. She was nominated several times for the Spellemanspris (Norway's equivalent of the Grammy) and won twice; the second time, according to the MIC, she appeared on every recording nominated in her category.