Tellefsen was born in Malvik Municipality on 23 August 1930, a daughter of Johan Fredriksen and Anna Bergljot Smaage.

[1] Tellefsen made her stage debut at Det Norske Teatret in 1956.

She worked for Fjernsynsteatret in its early days, during the 1960s, and she was assigned to Oslo Nye Teater 1969 to 1973.

She was co-founder and later artistical director of Telemark Teater, and was assigned to Nationaltheatret from 1981 to 2001.

[3] She received the Amanda Award in 1996 for her role in the film Kristin Lavransdatter.