Sydney Quiseng (née Sierota) is the lead singer of Echosmith, an indie pop band that she formed with her siblings. She also helps to write songs for the band.

In August 2024, Sydney changed her professional name from Sydney Sierota to Sydney Quiseng, adopting the last name of her husband Cameron Quiseng, and began hinting on social media that she would be starting a solo career. Her debut single as a solo artist, “Wonder”, was released on September 13, 2024. Over the next 8 months, she released the singles “Guilty”, “Phases”, “I Need Findin'” and “Leftover Coffee”, all of which appeared on her debut EP Phases in June 2025.

In addition to being a musician, Sydney is a model and has her own clothing line.