McClelland is the earliest elected Senator and federal Labor parliamentarian still alive[1], and along with Paul Keating is the last surviving minister who served under Gough Whitlam.

His father was a farmer, union organiser, and ALP politician who served two terms in the Parliament of New South Wales (1920–1927 and 1930–1932).

He was stationed for periods in New South Wales, Queensland, and the Northern Territory before being discharged in January 1947 with the rank of corporal.

In August 1981, McClelland was elected Chairman of Committees in the Senate, adding the title Deputy President in October.

He defeated National Country Party senator Douglas Scott by one vote with the aid of the Democrats, marking the start of the convention that the position is held by the opposition.

In 1985 and 1986, he was represented by lawyers at the trials of Lionel Murphy, a judge of the High Court and former ALP senator, where concerns had arisen over whether parliamentarian witnesses could be examined on their conduct in parliament.