Hildigunnur Rúnarsdóttir was born in 1964 in Reykjavík. She studied at the Department of Music Theory at the Reykjavík College of Music, majoring in composition.  Her teachers were Thorkell Sigurbjörnsson and Atli Heimir Sveinsson. She then studied composition in Hamburg with Professor Günter Friedrichs and in Copenhagen with Svend Hvidtfelt Nielsen. Hildigunnur has worked extensively with various choirs, including the chamber choir Hljómeyki. Her repertoire is extensive, with choral works and chamber music at the forefront. She has written a vast number of choral works and songs, with Vorlauf being one of her best known works. Other works include the children operas Peanut-Jon and the Golden Goose and Gilitrutt, Mixed Dances for Orchestra, Concerto for Violin and Orchestra, Mass of Guðbrandur, for choir, soloist and orchestra (nominated for the Icelandic Music Awards in 2003) and music for the documentary films of Ásdís Thoroddsen. Hildigunnur's works have been selected for the CDs of the renowned choir festival Europa Cantat. Hildigunnur has twice been chosen as composer of the month by the respected choral society Choralnet.org and also received the Silver Platter Award from the Composers' Society, also from Choralnet. Hildigunnur's works are regularly performed around the world.

Hildigunnur works as a composer, teacher and singer in Reykjavík.