Rau was admitted as a solicitor and barrister of the Supreme Court of South Australia in 1981. He worked as an adviser to Hawke government ministers Mick Young, Michael Tate and Neal Blewett from 1985 to 1988. He served as a Commonwealth nominee on the South Australian Legal Services Commission. He has also served on the ALP State and National Executives.

Before his service as a political adviser, Rau worked as a solicitor at Duncan Groom, Carabellas & Hannon. From 1988 to 1997 he worked as a solicitor and barrister at the firm of Johnston Withers, becoming a partner. Rau joined the independent bar and Murray Chambers in 1997. ^{[citation needed]}

Rau has appeared as counsel in the South Australian Industrial Relations Commission, the South Australian Industrial Relations Court, the Workers Compensation Tribunal, the Supreme Court of South Australia (including once as Attorney-General), the District Court of South Australia and the Federal Court of Australia.

His first political experience as a Labor candidate occurred at the 1993 federal election, when he stood for the Division of Hindmarsh, where he was narrowly defeated by Liberal Party candidate Chris Gallus by 1.6 percent.

Prior to the 2002 state election, Rau contested Labor preselection for the safe seat of Enfield. The seat had previously been Ross Smith, held by Ralph Clarke, who had recently been deposed as the party's deputy leader. The local party branch chose Clarke who received 60 of 74 votes. However, the party's state executive stepped in and installed Rau as the pre-selected candidate. Clarke ran as an independent Labor candidate, receiving a respectable 23 percent of the vote; however, Clarke narrowly fell short of overtaking Rau and winning the seat on Liberal preferences. Rau easily won the seat with a 35.9 percent primary and 65.9 percent two-party vote. He is aligned with Labor's right faction.^[1]

Rau gained publicity in 2004 over his involvement in the Real Estate Industry – Reform bill, which was designed in an attempt to stop industry practices such as dummy bidding at auctions.

The 2006 state election saw Rau retain Enfield with a 63.4 percent primary and 74.5 percent two-party vote. At the 2010 state election, Rau suffered a swing to finish with a 52.6 percent primary and 60.5 percent two-party vote.

Rau became Attorney-General when Michael Atkinson stepped down from the position following the 2010 election.^[4] Like his predecessor, Rau has also been described as a social conservative.^[5]

Rau expressed approval for the introduction of an R18+ video games classification following the resignation of Atkinson.^[6] The issue had been one for which his predecessor Atkinson received significant media attention.^[7] Rau appeared to be taking a different view to his predecessor and considered allowing an introduction of an R18+ classification.^[8][9]

In February 2011, Rau was elevated to Deputy Premier following the resignation of Kevin Foley from the position.^[10]

On 22 November 2016, Rau was appointed a Senior Counsel by the Supreme Court of South Australia.^[11]

In addition to Deputy Premier and Attorney-General, in the Cabinet of South Australia Rau held the ministerial portfolios with responsibility for justice reform, planning, industrial relations, child protection reform, the public sector, consumer and business services, and with responsibility for the City of Adelaide.^[12]

Rau attended Henley High School.^[13]

• "Rau, John". Former members of the Parliament of South Australia. Retrieved 19 August 2022.
• Parliamentary Profile: SA Labor website
• "Enfield: Adelaide Inner Northern Suburbs". ABC News Online. Australian Broadcasting Corporation. 2006. Retrieved 31 January 2011.
• "South Australian House of Assembly Election 2006: Enfield". The Poll Bludger. Archived from the original on 16 July 2011. Retrieved 31 January 2011.
• "Ralph Clarke runs as independent". ABC News Online. Australian Broadcasting Corporation. 2 March 2006. Retrieved 31 January 2011.