Siân Rebecca Berry is a British politician who served as a co-leader of the Green Party of England and Wales alongside Jonathan Bartley from 2018 to 2021, and as its sole leader from July to October 2021. From 2006 to 2007, she was one of the Green Party's principal speakers.

The Leader of the Green Party of England and Wales is the most senior political figure within the Green Party of England and Wales. The role was introduced alongside that of deputy leader in 2008. Prior to this, the party's public spokespersons were principal speakers. There were two principal speakers, one female and one male, who were elected annually at the Green Party's Autumn Conference and held no vote on the Green Party Executive (GPEx).