Nketiah had been with Arsenal for almost a decade, but is set to make his first appearance for Crystal Palace against Leicester this Saturday.
"I'm really excited for my Selhurst debut, and hopefully I can make it one to remember," he said.
"I know what it means to be a South Londoner. (Arsenal) was like a home to me, but I think you just want to take that next step in your career.
"Crystal Palace is a wonderful place. I want to improve, play more minutes, and hopefully help the team as much as I can."