Currently Mr McMullan is the Federal Shadow Minister for Industrial Relations. He entered parliament in 1988 as the representative of the Australian Capital Territory in the Senate. His ministerial appointments include being the Parliamentary Secretary to the Treasurer from 1990. Mr McMullan has served on several committees including being Chairman of the Senate Select Committee on Administration of Aboriginal Affairs and the Senate Committee for Foreign Affairs, Defence and Trade.
Mr McMullan was State Secretary (WA) of the ALP from 1975 to 1981 and ALP National Secretary from 1981 to 1988.