Matthildur Anna Gísladóttir completed a Bachelor's degree in Piano Performance at the Iceland University of the Arts. She then continued her studies at the Royal Academy of Music in London, where she earned a Master's degree in Accompaniment in 2009. In 2014, Matthildur completed a Master's degree in Opera Coaching at the Royal Conservatoire of Scotland (RCS). She studied there on a full scholarship and received the James H. Geddes Repetiteur Prize.

During the 2014–2015 academic year, Matthildur worked as an opera coach at RCS.

Matthildur has performed extensively in Iceland and abroad and has been involved in numerous opera productions, including with Kammeróperan, Óperudagar, the Icelandic Opera, British Youth Opera, the Royal Conservatoire of Scotland, Scottish Opera, and the Lyric Opera Studio in Weimar.

She currently teaches in the Department of Music at the Iceland University of the Arts.