The net cost to RBS of $4.75 billion is largely covered by money already set aside, said the bank which was rescued by the British government in the world's largest bailout at the height of the financial crisis in 2008.
He called the settlement an "important step forward" in resolving one of the bank's biggest legacy problems.
Under the terms of the settlement, RBS will be reimbursed US$754m of the US$5.5bn related to "indemnification agreements with third parties".
Laith Khalaf, senior analyst at Hargreaves Lansdown, said 10 years on from the financial crisis, RBS and the United Kingdom taxpayer are still counting the cost of the bank's former misdemeanours.
"The elephant in the room is the US Department of Justice fine, which is likely to be sizeable, and is subject to a high degree of uncertainty".
McEwan has been at pains in recent months to insist RBS has put its legacy issues behind it.
As previously disclosed, RBS continues to cooperate with RMBS related investigations and proceedings (both formal and informal) by federal and state governmental law enforcement and other agencies including the US Department of Justice ("DOJ") and various other members of the RMBS Working Group of the US Financial Fraud Enforcement Task Force.
The FHFA previously recovered $17.87 billion to resolve most of those lawsuits, including $5.83 billion from Bank of America Corp and $4 billion from JPMorgan Chase & Co.
RBS has already set aside most of the funds needed to resolve allegations made by the Federal Housing Finance Agency that it packaged and sold risky loans worth over $30 billion to US mortgage giants Fannie Mae and Freddie Mac.
The FHFA contended that in buying the mortgage-backed securities from RBS, Fannie Mae and Freddie Mac relied on false and misleading statements contained in offering documents, leading them to suffer massive losses. These were complex securities backed by cash flows from mortgages that Fannie Mae and Freddie Mac bought and which contributed to the failure of the two mortgage giants when the housing market collapsed. The bank is not required to offer an admission of guilt as part of this settlement.
RBS shares traded up over 1% premarket.