[1] Siem studied piano with Nils Larsen, Erling Westher and Ivar Johnsen.

He made his concert debut as pianist in 1938, and toured widely in Norway and internationally until his playing career was interrupted by an injured elbow.

He started writing music for film and theatre, worked as kapellmeister and conductor, contributed to the Norwegian Broadcasting Corporation, and was a columnist for the newspaper VG.

An active participant in the Friends of Folk Song Club [no], he co-edited several songbooks, jointly with Thorbjørn Egner and Yukon Gjelseth.

His publications further include the cookbook Kåres nam-nam-bok for kløner og duster (1974) and the memoir books Bingo (1978) and Klokkene ringer for meg (1979).