Sian was re-elected in 2021 for a second term as an Assembly Member. Sian has lived in London since 1997 and has worked as a medical copywriter, PA, website manager, project manager for a digital start-up, author and transport campaigner before being elected as a Member of the London Assembly in May 2016.

Sian has worked on the Assembly to strengthen the rights of renters and people who live on estates, as well as helping to win new funding for youth services in London. She is currently Chair of the Housing Committee, Deputy Chair of the Planning & Regeneration Committee and sits on the Transport Committee.

Sian has been a local councillor in the Highgate ward of Camden since 2014. She has also served two terms as co-leader of the Green Party of England and Wales.