In the firm's first-half results today, it was announced that Mr McEwan would take over the role on 1 October, having initially joined RBS last September as UK retail chief executive.
Mr Hester announced he would be stepping down from the role in June and since then RBS has conducted an international search for candidates.
Philip Hampton, RBS chairman, said: "This is a job that is among the most important and challenging in the business world, and Ross has shown that he has the drive and capability to take it on. I conducted an international search for this position so our internal candidates could be benchmarked against the very best in the market. Ross was the strongest candidate and I am delighted he has been appointed."
Mr McEwan said: "I look forward to leading RBS as it plays its full role in supporting our customers. We have a lot of work ahead of us and I'm very much looking forward to getting started."
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RBS reported a first-half pre-tax profit of £1.4bn, compared to a loss of £1.7bn during the first half of 2012. Group operating profit of £1.67bn, up five per cent from the same period in 2012.
The firm said this was the first that RBS had posted a profit in two consecutive quarters since the financial crisis.
Core operating profit was £2.5bn, down 17 per cent from the same period in 2012 due to the reduction in markets income. Retail and commercial profits were down four per cent with improved operating results in UK retail but weaker results in international banking.
Charges for redress and regulatory investigations totaled £620m including £185m for payment protection insurance redress. This brings the total amount paid out in PPI redress to £2.4bn.

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