Ruby followed in her mother's footsteps by becoming a high fashion model. She signed to Nous Model Management in Los Angeles and Select Model Management in London. Her older half-sister Kimberly Stewart is also a model. Ruby did runways for Karen Walker for her Spring/Summer 2006 collection for London Fashion Week during 2005. Walker praised her "unpretentious youthfulness".
In the summer of 2010, Ruby formed the Los Angeles-based band, Revoltaire, along with Jason Yates (guitar,keys) and Chris Cano (drums). The band completed an album's worth of material titled “Painted Hour Glass", with Ruby as the vocalist and lyricist. In 2012, Revoltaire disbanded.
On March 13, 2016, she performed in her first music festival with band mate Alyssa Bonagura at the CMC Rocks festival in Queensland, Australia. Billing themselves as The Sisterhood, the two performed a one-hour set with backing by the Morgan Evans band.
- Cheng, Derek (September 21, 2005). "Rod's daughter wears it well for Karen Walker". The New Zealand Herald.
- "Ruby Stewart sparkles in new campaign for Ultimo lingerie brand". Daily Mail. London. November 29, 2007.
- "Rod Stewart's daughter Ruby turns lingerie model". Hindustan Times. New Delhi. September 20, 2007.
- Oldenberg, Ann (January 11, 2012). "Sofia Vergara: Another naked Golden Globes bet?". USA Today.
- Darren Cartwrigh (10 March 2016). "Rod Stewart's daughter plays CMC Rocks". Yahoo.com. Australia: Seven News. Archived from the original on 11 March 2016. Retrieved 11 March 2016.