[3][4][5] In the 1996 federal election, Rattenbury was the Greens candidate for the newly created Division of Namadgi in the southern suburbs of Canberra.

After the distribution of preferences, Rattenbury was defeated by both Labor's Wayne Berry and the Australian Democrats' Roslyn Dundas.

Under the agreement, the Greens secured a range of policy outcomes in the areas of schools and education, health service provision, housing, public transport and gay rights.

[16][17] While on the cross bench in the 7th Assembly, Rattenbury was Greens spokesperson in the portfolios of Attorney-General, Environment, Climate Change and Water, Energy, Police and Emergency Services, Tourism, Sport and Recreation.

With the election resulting in a hung parliament, Rattenbury, who held the balance of power, announced he would support Katy Gallagher and the Labor Party in the formation of government.

The ACT Labor Caucus agreed to appoint Rattenbury as a minister in Gallagher's five-member cabinet, and to support 100 Greens policies.

[19][20] Although a member of the Barr government, he reserved the right to withdraw from Cabinet discussions on divisive issues and vote independently in the Assembly.