Born in Corwen, North Wales, Green studied at Aberystwyth and Manchester Metropolitan Universities and was chair of IR Cymru (now Welsh Young Liberals). In 2014 she founded the marketing and communications company Green and Ginger. She fought Ynys Môn at the 2005 general election and Arfon in 2010. Selected to fight the Chesham & Amersham by-election she won the seat with a majority of 8,028 on a swing of 25.2% from the Conservatives. In July 2022 Sarah Green was appointed Liberal Democrat spokesperson for International Trade and for Wales.