During her time as an MP she served variously as the Green Party spokesperson on Education, Water, Toxics, Te Tiriti o Waitangi, Mining (Terrestrial), Forestry, Civil Defence, Disability Issues, Women's Affairs, Arts, Culture & Heritage, and the Community & Voluntary Sector.

She has been placed high on the Greens' list for several years, just missing getting into Parliament on several occasions.

She was elected as a Green Party MP and gained the fourth highest number of candidate votes in the East Coast electorate.

In June 2009, Delahunty's Customs and Excise (Sustainable Forestry) Amendment Bill, which would have prohibited the import of timber produced unsustainably or illegally, was drawn from the member's ballot.

On 15 December 2016, she announced alongside Steffan Browning that she will not be seeking re-election in the 2017 general election.