During the 1970s, she was a member of the song group Mixed Media, which also included her sister Lena Olin. Between 1979 and 1989 she was active at the Oktoberteatern in Södertälje. Since then she is a freelancer, but often works in the independent theater group Musikteater89. Olin has worked as a director and put on several youth performances in his hometown Stallarholmen. She has also directed Kent Andersson's "Hemmet " and "Momo - kampen om tiden" by Michael Ende.

Olin sings and has her own quintet: Kersti Olin Band with Erik Dahlbäck, Jan Sjöblom, Tommy Skotte and Anders Ekholm. She often collaborates with her sister Maggi Olin who is a composer and pianist.