NAB has now divested 100 per cent of GWB after disposing of its remaining 16,486,114 shares in the US bank.
The divestment is part of NAB chief executive Andrew Thorburn's strategy to focus on the bank's Australia and New Zealand businesses.
NAB has also set a deadline of the end of the 2015 calendar year to completely exit its UK banking business, Clydesdale Bank.
Mr Thorburn announced the IPO and sale of GWB on 29 August 2014, saying at the the time that NAB intended to concentrate on its "core business" in the Asia-Pacific.
"Having a clear focus on our Australian and New Zealand business will allow us to invest in our priority segments, to deliver a better experience for customers and improved returns to shareholders," Mr Thorburn said in an ASX statement.
The net proceeds from the full sale of GWB will deliver $1.464 billion to NAB, representing a $396 million loss relative to the bank's book value.
"$329 million of this loss from the initial public offering and second offering were treated as equity transactions and, consistent with relevant accounting standards, recognised in retained earnings in the period of the transactions," NAB said.
"The final offering is expected to incur a $67 million loss on sale in the September 2015 full-year accounts which will be reported as a discontinued business outside of cash earnings.
"Full divestment of all common shares in GWB is expected to increase the group's Common Equity Tier 1 ratio (CET1 ratio) by approximately 34 basis points and is broadly consistent with estimates provided at the 1H15 result for achieving a pro forma CET1 ratio of approximately 10 per cent.
NAB said the benefit will arise when it is no longer controls GWB for US bank regulatory purposes, which the bank is in the process of confirming.