She grew up in Luleå, where her musical career began with piano, violin, organ and singing lessons as well as solid choir training in the cathedral's choirs.

Karin Oldgren began her studies at the Royal Academy of Music in 1986 as a church musician, with a major focus on organ playing, from which she graduated in 1991. Gradually, however, she settled on a new musical track and four years of conducting studies, for professors Anders Eby and Gustaf Sjökvist in choir and Kjell Ingebretsen in orchestra, leading up to her diploma concert as choral conductor in 1996.

In January 2022, Oldgren took over as organist as well as conductor and artistic director of Petri Sångare and St. Petri's youth choir in the Swedish Church in Malmö.