The accord is in the final stages of negotiation and is expected to be announced by the end of the first quarter, the person said.
The settlement would resolve a 2013 US Department of Justice suit accusing the ratings agency of misrepresenting as safe high-risk securities linked to subprime mortgages.
The US argued S&P's ratings of the securities were too positive because it sought to win business from investment banks packaging the toxic mortgage-linked bonds that were at the heart of the 2008 financial crisis.