Siewert was first elected to the Senate at the 2004 election and commenced her term in July 2005. She was re-elected for a second term at the 2010 federal election, and again at the 2016 double dissolution

She was prominently involved in the establishment and running of the Conservation Council of Western Australia, working for a number of years as its Coordinator, and was awarded the Bessie Rischbieth Conservation Award in 2003.

Siewert was Co-Convener of The Greens (WA) from 2002 to 2004.

Born in Sydney, Siewert’s family moved to Perth when she was 13. She later studied a Bachelor of Science, majoring in Agriculture, at the University of Western Australia, and worked with the Western Australian Department of Agriculture as a research officer in 1984–87.

Rachel Mary Siewert (born 4 November 1961 in Sydney, New South Wales) is an Australian Greens politician who was elected to represent Western Australia in the Australian Senate at the 2004 federal election.