Greece's rating now stands at "CCC+" in an upgrade announced Tuesday. That classification means Greece is still on shaky financial ground, but less likely to face an immediate credit crisis.
S&P had previously rated Greece as "CCC-," a category signalling that loan payments are likely to be missed within six months.
Greece was on the brink of reneging on part of its national debt of 320 billion euro ($347 billion) earlier this month until agreeing to a series of concessions to obtain short-term financing from other European nations.
S&P still believes there is a one-in-three chance that Greece will leave the eurozone.