It is understood Glasgow-based Mr Thorburn travelled to Australia up to six times a year to go to top level committee meetings.
The change of duties is expected to give him back several weeks' worth of time once long-haul travel, preparation, reading and other duties are factored in.
The move comes a few months after National Australia Bank (NAB) announced a major revamp of its UK operations which will lead to 1400 job losses by the end of 2015 plus the closure of several financial solutions centres and some back office locations.
Mr Thorburn, chief executive at Clydesdale and Yorkshire banks, said: "We are moving forward with our strategy to become a stronger and more competitive business following our strategic review announcement at the end of April.
"My priority has always been the UK business and stepping down from the group executive committee will enable me to dedicate all of my time to this important restructure programme.
"The steps we are taking are difficult, particularly for our employees, but we have the right plan and I am confident what we are doing is in the best long term interests of the organisation and our customers."
Mr Thorburn will continue to report to NAB chief executive Cameron Clyne.
NAB said in a third quarter trading update UK operations were still dragging on its overall business.
Unaudited cash earnings before exceptional items for the three months to June this year were stable at A$1.4 billion (£930 million).
Revenue dipped 1% due to funding costs in the UK and lower income from the markets and specialised group assets arm although personal banking reported strong growth.
Overall charges for bad and doubtful debts were down 7% to A$524m (£350m) but there was an unspecified increase in the business banking division.
Expenses had dropped while employee numbers were also lower, although NAB did not give specific details.
In the UK results were "weaker" because of lower revenue and increased funding costs.
The charge for bad debts was down but remained "elevated" with assets continuing to decline in the troubled commercial real estate portfolio.
Mr Clyne said: "NAB delivered a stable result for the quarter and made further ground against its strategic agenda to strengthen the Australian franchise, which has been the Group's unwavering focus since 2009.
"This quarter's result is set against a backdrop of ongoing challenges in the global economy with continued uncertainty in the eurozone and the United States, volatility in global financial markets, and slowing growth in big emerging economies.
"Although subdued business and consumer confidence continue to affect the Australian economy, we remain positive about the outlook."
Credit Suisse analyst Jarrod Martin was concerned about the weakness of assets in the UK and said NAB earnings were lower than expected.
