[3] He was active in the movement against the Vietnam War and was conscripted for military service in 1968 but successfully argued in court that he was a conscientious objector.

In December 1987 he announced he would seek ALP preselection to fill the casual vacancy caused by Susan Ryan's resignation from the Senate.

[6] On 16 February 1988,[7] McMullan was chosen by a joint sitting of the House of Representatives and the Senate to fill a casual vacancy in the representation of the Australian Capital Territory in the Senate, caused by the resignation of Susan Ryan.

[10] On 6 February 1996 he resigned his Senate seat in order to contest the Division of Canberra in the House of Representatives at the March election; he was successful.

He was the first person to represent the Australian Capital Territory in both houses of federal parliament.

[citation needed] Following the election of Kevin Rudd on 4 December 2006 as Opposition Leader in place of Kim Beazley, McMullan returned to the front bench in the junior role of Labor spokesperson on Federal-State Relations,[11] the reform of which was one of Rudd's declared priorities.

[12] When the First Rudd Ministry was sworn in on 3 December 2007, McMullan was given the junior post of Parliamentary Secretary for International Development Assistance.