She was appointed as a Greens member of the New South Wales Legislative Council on 22 February 2017 to fill a casual vacancy resulting from the resignation of Jan Barham, and served until her defeat at the 2019 state election.

[3] On 22 February 2017, Walker was elected by a joint sitting of the New South Wales Parliament to fill a casual vacancy resulting from the resignation of Jan Barham.

[6] On 6 December 2017, Walker was arrested along with 16 other people including fellow NSW Greens MLC Jeremy Buckingham after taking part in a blockade of Adani’s Carmichael coal mine rail construction site at Belyando, in Queensland.

I was proud to stand with traditional owners who have said 'no means no' to Adani, and made it clear they will not be surrendering their land and water to this coal corporation.”[8] Since being elected, Dawn Walker has campaigned for the creation of a new 315,000 hectare Great Koala National Park in the Coffs Harbour hinterland[9] and for an end to native forest logging in New South Wales.

[10] Her preselection was controversial, with the returning officer of the ballot identifying "areas of concern" about the integrity of the process, and claims that Walker had broken party rules by using its email lists for campaigning purposes.