Milly Alcock was born on April 11, 2000, in Sydney, New South Wales, Australia12. She grew up in Sydney's inner-west with two younger brothers in what she describes as a "non-arty family"3. Alcock's passion for acting was ignited at a young age when she played Little Red Riding Hood in her school's production of "Little Red Rocking Hood"4.

Alcock attended Stanmore Public School before enrolling at Newtown High School of the Performing Arts4. Her independent spirit was evident from an early age; she recalls telling her mother at four years old that it was time for her to go to "big school"5. This determination carried into her teenage years when she made the bold decision to drop out of high school in 2018 to pursue her acting career full-time after being cast in the series "Upright"24. Despite the risks, Alcock viewed this opportunity as more valuable than completing her formal education, a decision that would ultimately pave the way for her breakthrough in the entertainment industry53.

Milly Alcock's breakout role came in the Australian comedy-drama series "Upright," where she played Meg, a runaway teenager. The show, which premiered in 2019, follows Meg and Lucky Flynn (Tim Minchin) as they embark on a road trip across the Australian outback to transport a piano12. Alcock's portrayal of the gritty, foul-mouthed Meg earned her critical acclaim and a nomination for Best Comedy Performer at the 10th AACTA Awards3.

The role in "Upright" was a pivotal moment in Alcock's career, as she made the difficult decision to drop out of high school in her final year to pursue it. She described the experience as "incredibly exciting," stating, "I was 18. I just dropped out of school and I went and I traveled around Australia for three months shooting a TV show"4. This decision paid off, as her performance in "Upright" not only showcased her acting range but also opened doors to larger international productions, ultimately leading to her casting in "House of the Dragon"12.

Milly Alcock's breakthrough role as young Rhaenyra Targaryen in "House of the Dragon" catapulted her to international fame. Her portrayal of the headstrong princess garnered critical acclaim, with many considering her performance a highlight of the series12. Alcock's nuanced acting and expressive face brought depth to the character, earning her a nomination for the Critics' Choice Television Award for Best Supporting Actress in a Drama Series3.

Despite the show's massive scale, Alcock approached the role with dedication and humility. She revealed that she was washing dishes at a restaurant in Sydney when she learned she had landed the part2. The experience of working on such a high-budget production was initially overwhelming for Alcock, who noted that the entire budget of her previous Australian shows was less than that of a single "House of the Dragon" episode4. However, she embraced the challenge, drawing parallels between her own journey and Rhaenyra's navigation of an unfamiliar world4.