The visitors looked the better side throughout on Saturday and got the goal their performance deserved 10 minutes after the break when the lively Sean Scannell broke into the box and his low cross was turned in by McCarthy.
Ipswich's best moment came at the end of the first-half when Jay Emmanuel-Thomas saw a shot tipped over the bar by Palace goalkeeper Julian Speroni and the home side had Aaron Cresswell dismissed late on for a second yellow card.
The win extended Palace's winning run to three matches and was made even sweeter as they kept a third consecutive clean sheet in the league for the first time in over two years.
Both sides went into the game in fine form but it was the visitors who looked brightest early on and Wilfried Zaha got away down the right and fired in a dangerous cross which Ipswich defender Damien Delaney deflected just wide of the far post.
Zaha was giving the Ipswich defence all sorts of problems and he got to the byline before cutting the ball back for Kagisho Dikgacoi who completely miskicked when he should have at least got a shot on target.
Ipswich eventually began to find their rhythm and Carlos Edwards did well down the right before whipping in a fine cross which was headed wide by the onrushing Lee Bowyer.
Five minutes before the break a corner from Scannell found Glenn Murray and his goalbound shot was cleared away by Delaney.
At the other end a fine Ipswich break resulted in Emmanuel-Thomas firing in a shot from the edge of the box that was superbly tipped over by Speroni.
Ipswich suffered a blow just after the break when Delaney was forced off injured and replaced by Ivar Ingimarsson.
Palace looked to take the initiative and Jonathan Parr hung in a cross which was met by Murray but his header went onto the roof of the net.
With 55 minutes gone the visitors went in front when a free-kick from Scannell was cleared back to him and he drove into the box before whipping in a low cross which McCarthy toe-poked into the roof of the net.
Ipswich manager Paul Jewell responded by bringing strikers Michael Chopra and Jason Scotland on for Jimmy Bullard and Nathan Ellington but it was Palace who continued to dominate.
The lively Scannell evaded a weak challenge from Keith Andrews and burst into the box before firing in a shot from a tight angle which was saved by Ipswich goalkeeper David Stockdale.
The home side were struggling to break down the resolute Palace defence and Chopra had a hopeful shot blocked by Nathaniel Clyne.
With eight minutes remaining Emmanuel-Thomas's free-kick was tipped over by Speroni and Cresswell saw red for a second yellow card to complete Ipswich's misery.