SYDNEY—Australian Treasurer Jim Chalmers on Thursday announced the biggest reforms of the Reserve Bank of Australia in three decades, moving to bolster the level of expertise involved in the setting of interest rates, while striking hard at what many critics say is the closed culture of the central bank.

The changes will see the RBA adopt a monetary-policy committee structure that mimics in many ways processes now in place at the Bank of Canada and the Bank of England, while the number of policy meetings each year will be…