[4] He is a patron of the State Library of New South Wales as a foundation senior fellow[7] and has been a member of the NSW Health Clinical Ethics Advisory Panel since 2003.

[4][8] He was a leading legal counsel representing tobacco companies in their unsuccessful fight against the Australian government's plain packaging legislation.

The report was damning of the maladministration that characterised the overseeing Murray-Darling Basin Authority, describing their decision-making as “incomprehensible” and “indefensible”.

In 2019 Walker successfully acted in the appeal to the High Court of Australia of Cardinal George Pell, whose child sex abuse convictions were overturned on 7 April 2020.

[16] In April 2020 Walker was appointed to a Special Commission of Inquiry to "investigate all matters and agencies involved with the Ruby Princess' departure and its return to Circular Quay on March 19".