Sadie enjoyed a career as a child actress through many voice-over parts, making her screen debut when she was eight, playing Penny in the BBC film, Royal Celebration. She is best-known to Doctor Who fans for her role in both series of Sarah Jane Smith audio dramas produced by Big Finish in 2002 and 2006. She won much critical acclaim for the role of the wheelchair-bound Planet 3 researcher, Natalie Redfern, particularly in the story Test of Nerve.

She completed courses with the National Youth Theatre, the Royal Court Theatre's Young Writer's Programme, and RADA's Shakespeare Course. She earned a BA in English and Related Literature, and graduated with honours.

Sadie turned from acting in 2011. “After University, I went to drama school and was actually in my final term when mum died. This obviously impacted how I looked at my future and I decided to switch to writing instead so that I could have a little more control and flexibility to be around for my dad.” She is currently working on an original Young Adult novel, having already contributed to anthologies. In 2014 she was a finalist for the Glass Woman prize with Mirandolina.
Sadie is no stranger to Doctor Who, of course. Her father is actor Brian Miller, who has appeared in both Doctor Who and The Sarah Jane Adventures, and her mother is Doctor Who legend Elisabeth Sladen, the actress who won the hearts of millions of Doctor Who fans in the 1970s as Sarah Jane Smith, and once again in 2005 when she brought Sarah back to the modern era of Doctor Who. Elisabeth Sladen sadly passed away in 2011, which led to Sadie distancing herself for some time from Doctor Who fandom.

“I needed time to mourn, to be there for my dad. The constant reminders of my mum, obviously very hard to avoid, were just too painful. But now I feel that the time is right to reconnect with Doctor Who, and the fans,” said Sadie. “My dad did so last year with an appearance in Peter Capaldi’s first episode, and so now it’s my turn. It’s exciting to be writing my first novel, and that it features the Brig adds another layer of importance. He, in the form of Nicholas Courtney, was there when mum debuted as Sarah in 1973, and she was there for his very last on screen appearance as the character in 2008. So in many ways this is important.”