Külli started her studies at Music Department of Pärnu High School of Humanities (Tiina Palmer), then at the Tallinn Conservatory (Urve Tauts). In 1994 took place her debut as Marcellina in “Le Nozze di Figaro” at the Pärnu Opera (conductor Rolf Gupta, directed by Elmo Nüganen). There followed the “Pierrot Lunaire” by Arnold Schoenberg in Pärnu Opera (conductor Andrus Kallastu, directed by Rein Laos), role of Sharon in Masterclass by T.MacNelly at the Endla Theater (directed by U.Vilimaa). Role of the third slave in “Elektra” by Richard Strauss at the Pärnu Opera in ( A.Kallastu, directed by R.Laos).
Külli graduated from Piacenza Conservatory in Italy, in class of Adelisa Tabiadon. Her studies continued at the Milan Academy of Music with Bianca Maria Casoni. Külli participated in master classes of Matti Pelo, Leyla Gencer, Luciana Serra, Claudio Desderi, Katia Ricciarelli and Enzo Dara. She has received recognition in several international singing competitions: Roero in Musica, Nino Carta of Moncaleri, Titta Ruffo of Pisa, Ismaele Voltolini of Mantua, Riccardo Zandonai of Riva del Garda and Voice Masters of Monte Carlo.