The first House of Representatives was elected on 30 March 1901. All the members elected to that First Parliament therefore had equal seniority. It follows that there could not be a "longest-serving member" until only one member from the First Parliament was still in the House. That occurred on 8 April 1935 with the death of David Watkins.
Since that date the longest-serving members of the House of Representatives have been:
4 January 1982 and 21 April 1983 several members had equal lengths of service.