[citation needed] Tanner began his career as an articled clerk and solicitor at Holding Redlich Lawyers in Melbourne.

He remained a member of the Shadow Ministry, despite numerous changes of leadership, continuously until the election of the Rudd Labor government in November 2007.

In 1999, he wrote a book entitled Open Australia, which explored how information technology could be used to enhance social justice and economic equality; and he also wrote a number of articles on targeted, "micro" ways of addressing globalisation and the decline of large-scale manufacturing, in which he suggested there was little substance to the notion put forward by neoclassical economists of a "simulated free market" in East Asian economies that explains their "emergence" (see 1997 Asian Financial Crisis).

In the second leadership spill in December 2003, Tanner supported Beazley,[3] who lost the party-room ballot to Mark Latham.

After the October 2004 federal election, Tanner was thought to be a candidate for the position of Shadow Treasurer, which had been vacated by Simon Crean.

He subsequently released a brief statement, stating that he had "no complaint about how Mark Latham has dealt with [him] personally", but adding that he had "serious reservations about the emerging Labor response to our latest election defeat.

[7] Tanner has been appointed as a Vice Chancellor's Fellow and adjunct professor at Victoria University,[8] and a special adviser to financial firm Lazard Australia.

[9] In 2011, the Chartered Institute of Procurement and Supply (CIPS) accorded him the rare distinction of an Honorary Fellowship (FCIPS), the first to be bestowed outside of the UK.