O'Sullivan jets off to Buenos Aires on Saturday for Ireland's two-Test tour of Argentina with a largely second-string squad, including Carney, hoping to push for a World Cup-squad place.
On his decision to call up former Wigan and Great Britain winger Carney, O'Sullivan said: "I wouldn't have called Brian up unless I thought he was good enough.
"I would still be guarded about it but from what I have seen of him with Munster, he is a very good player and is a footballer who has played at the highest level and has made the transition pretty flawlessly.
"He played on the wing in rugby league and does the same in union. It's probably the easiest transition to make. I believe he will acquit himself well and it is a challenge for him. The next step up is to Test level."
O'Sullivan will not be tempted to try Carney out in the full-back role during the Argentina tour.
"It was great for Brian to play full-back for Munster recently but the Magners League is not international rugby and it would not be fair to him to throw him in at the deep end at full-back in Test rugby.
"This tour is not about any experimental tactics. We will keep it simple and hopefully we will be wiser at the end of it.
"It's not a long tour and we have players being rested and that gives fellas a great opportunity to throw down a marker for the World Cup.
"This tour is the real deal for a lot of guys to put their hand up for a World Cup place.
"For that reason it is a very important tour and the players know that and it's not about intensity in training. It is about holding them back."