She is a graduate from the Norwegian Academy of Music, and performs with a variety of rock and jazz bands, including her own Hedvig Mollestad Trio, Bronco Busters, Songs and Sweet Potatoes, and VOM (as "Mester Pøggs").

Thomassen was awarded "The young jazz talent of the year" at Moldejazz in 2009, and played a gig within Jarle Bernhoft Band at the 2011 Kongsberg Jazzfestival.

(2011) leading her own trio, the music bears little resemblance to what she plays with Jon Eberson Group and the bands of Hilde Marie Kjersem and Jarle Bernhoft.

Since the trio's formation in 2009, HM3 has played many concerts and jazz festivals in both Norway and abroad and they have toured in Europe, Malaysia, Japan and the USA.

[7] In reviews of two of the band's albums, All About Jazz critique John Kelman states: In 2023, Mollestad formed a new trio, called Weejuns, with the keyboardist Ståle Storløkken from Elephant9, and the drummer Ole Mofjell.