[4][5][6] Her mother, Jenny Miller, was a ballet dancer and then a dance teacher and her father, Greg Heidke, is a high school principal.

[10][11] As an Opera Queensland Developing Artist, Miller-Heidke has performed as an understudy in productions, Sweeney Todd, Don Pasquale and Un ballo in maschera.

In July 2005 she made her solo professional operatic debut with Opera Queensland in the role of Flora in Britten's The Turn of the Screw.

[12] She was lead singer and songwriter with acoustic pop/folk band Elsewhere,[13] which formed in 2000, and released a self-titled extended play of original songs before breaking up in 2003.

[12] She performed at an annual event, Women in Voice, three times: in 2002, 2004 and 2005, where she shared the stage with Pearly Black, Margret RoadKnight, Jenny Morris and Chrissy Amphlett.

"[14] In June 2004 Miller-Heidke independently recorded and distributed her first EP, Telegram; from its seven tracks, five were written or co-written by her and two by her then-boyfriend, Keir Nuttall.

[16] Nuttall is the founding mainstay lead guitarist and vocalist in Brisbane-based progressive rock band Transport, which formed in 2001.

"[17] Miller-Heidke was preparing to sing the role of Mabel in Gilbert and Sullivan's Pirates of Penzance with Opera Australia in late 2005.

[14] Instead she turned from classical to pop music when "Space They Cannot Touch", a track from Telegram, became a hit on Australia's national youth radio network, Triple J and was named by station presenter Richard Kingsmill as his "pick of the week" in September.

[25][26] Australian musicologist, Ian McFarlane, felt it, "drew comparisons with Kate Bush and Tori Amos or 'like Nina Hagen, just with a much better voice'.

"[5] AllMusic's Jody Macgregor gave it four-out-of-five stars and observed, "When she uses her deceptively gigantic voice to sing about these little lives, Miller-Heidke achieves something that goes above and beyond the simple pleasures of pop music – a genuine profoundness.

[25] ARIA's Ian Wallace observed, "Although traces of her operatic style are recognisable in her songs, [she] has since decided to shy away from the opera circuit and make a dash for the pop scene.

[5] Miller-Heidke's second album, Curiouser, was released on 18 October 2008, which was recorded in Los Angeles, she worked with co-producers Nuttall and Mickey Petralia (Beck, Flight of the Conchords).

"The Last Day on Earth" received another nomination, for Most Popular Australian Single, in the newly installed public-voted categories at the ARIA Music Awards of 2010.

[5][40][41] The album was written and recorded on a lap top over several months, with Nuttall producing, in different locations in Australia, South East Asia and West London.

[5][47] It had been recorded at two studios in Melbourne and another in London: Nuttall co-producing with Lindsay Gravina (Jebediah, the Living End, Thirsty Merc).

[5][47] AllMusic's Ned Raggett gave it three-and-a-half stars and declaimed, "[it] doesn't surprise so much as reinvigorate, with [her] working of sometimes familiar tropes turning into one strong song after another.

Caught somewhere between cleanly energetic rock, piano-led moments, and [her] sometimes swirled vocals, the result is a remarkably enjoyable melange.

"[47] Rave Magazine's Josh Donellan observed, "It's still built on catchy pop hooks and melodies and will undoubtedly find itself at home on a few commercial radio stations, but the songs on this album also reveal a darker side to her songwriting.

2 – equal highest chart position with Curiouser – and provided three singles, "I'll Change Your Mind" (April 2012), "Sarah" (February 2013) and "Ride This Feeling" (July 2013).

[25] At the ARIA Music Awards of 2012 she was nominated for two more public-voted categories: Best Video for "I'll Change Your Mind" (co-directed by Miller-Heidke and Darcy Prendergast) and Best Australian Live Act for her tours in support of the album and related singles.

Miller-Heidke sang the screen-role of Amber in the world premiere of Michel van der Aa's opera Sunken Garden for the ENO in April 2013.

[59] She took on the role of "female protagonist" in van der Aa's interactive song cycle film, The Book of Sand (June 2015), based on the short story of the same name from 1975, by Argentine writer Jorge Luis Borges.

[63] She also debuted as a TV actress in the Australian Broadcasting Corporation (ABC) comedy opera miniseries, The Divorce (December) in the role of Caroline.

[75][76] Miller-Heidke and Nuttall also co-wrote the music for Phillips' 2018 production of Twelfth Night for the Melbourne Theatre Company where they were performed by Colin Hay.

[84] The Music AU's Guido Farnell, observed, "eleven nuggets of finely crafted pop tunes that are soft, dreamy and impossibly silky smooth whilst moving to compulsive grooves".

[87] The couple composed in collaboration with Connor D'Netto the monodrama The Call for Opera Queensland and Brisbane Festival 2022, featuring soprano Ali McGregor.

[91] In February 2024, Seven Network announced that Miller-Heidke would be joining the thirteenth season of the singing competition show The Voice Australia as a coach, replacing Jessica Mauboy.

Early in 2008 Campbell left to focus on her own band, Speed of Purple, and Nicole Brophy joined on guitar and vocals.

[8] She started dating the other group's lead singer and guitarist, Keir Nuttall, in the early 2000s while both attended Queensland Conservatorium of Music.