He has been an Australian Labor Party member of the Queensland Legislative Assembly since 2017, representing the electorate of Aspley.

[2] He was re-elected at the 2020 election, defeating LNP candidate and former Brisbane City Councillor Amanda Cooper with a 4% swing, increasing his margin to 5.4%.

After his re-election, Mellish was promoted to the position of Assistant Minister to the Premier for Veterans' Affairs, Trade and COVID Economic Recovery.

[3] Mellish assumed two additional ministries – Transport and Main Roads, and Digital Services – in December 2023.

This article about an Australian Labor Party member of the Parliament of Queensland is a stub.