The credit rating service revised its outlook to "Stable" from "Negative," which means it's less likely it will downgrade the country's debt in the near future.
It also backed the U.S. government's "AA+" long-term and "A-1+" short-term unsolicited sovereign credit ratings.
S&P downgraded the U.S. government's long-term credit rating in 2011 after a battle in Congress over whether to raise America's borrowing limit.
The ratings service said Monday that Congress managed to broker a deal late last year that allowed certain tax cuts to expire and cut spending. Meanwhile, S&P says the economy has started to improve and is expected to continue to do so.