The 1931 Auckland Rugby League season was its 23rd. The inaugural Fox Memorial Shield was won by Marist Old Boys who defeated Devonport United 12–5 in the final round to win by 2 competition points over the same side. This was Marists second ever first grade title after previously winning it in 1924. Devonport United did however win the Roope Rooster competition defeating Ponsonby United in the final. This was their second time winning the Roope Rooster after they won the inaugural title in 1915. They also beat Marist Old Boys to win the Stormont Shield Trophy for the second year in a row. Alongside these feats Devonport also won the inaugural reserve grade competition with a 5–5 draw in the final securing them the 1 competition point they needed to edge out Ponsonby United. Richmond Rover