She attended secondary school at Taupo-nui-a-Tia College and earned qualifications from the Waikato Institute of Technology, the University of Waikato and Massey University. She worked in the health field. She identifies openly as lesbian.
In the 2005 election Wall stood unsuccessfully in the Port Waikato electorate and occupied the 46th position on the Labour list. She became a Labour Party MP on 4 March 2008 to replace retiring list MP Ann Hartley.
In the 2008 election she stood in Tāmaki Makaurau, against Māori Party leader Pita Sharples. She failed to win the seat, and due to her low list placing (position 43) did not return to Parliament as an MP. However, in December 2010, she was selected to represent Labour in Manurewa for the 2011 election due to the retirement of George Hawkins. After Darren Hughes resigned from Parliament in April 2011, and people higher on Labour's list, such as Dave Hereora, Judith Tizard and Mark Burton, decided not to take up the list position, Wall was returned to Parliament as a Labour List MP serving in the 49th New Zealand Parliament. She subsequently won the Manurewa electorate and was returned to the 50th New Zealand Parliament; she had opted not to be on Labour's party list for that 2011 election. She was back on the list (in position 12) for the 2014 election but won her electorate comfortably.
In May 2012, Wall submitted a bill to legalise same-sex marriage in New Zealand to the private member's bill ballot, and it was subsequently drawn from the ballot and introduced to Parliament in late July 2012. On 29 August 2012, the Marriage (Definition of Marriage) Amendment Bill passed its first reading with a vote of 80-40. On 17 April 2013, the bill was passed into law, making New Zealand the 13th nation to allow same-sex marriage. At the third reading, Wall gave a speech likening the passing of the bill to Treaty of Waitangi settlement acts previously passed by the New Zealand parliament. Wall said the passing of the bill was like winning a "World Cup final".