Over 13 games this season, Barnes recorded six sacks, 12.5 tackles for loss, three quarterback hurries and 44 total tackles. The junior was an All-Big Ten honorable mention.
In three seasons, Barnes notched 98 tackles, 14.0 sacks and 26.5 tackles for loss. He was named the conference's freshman of the year in 2012.
"Can't believe I've walked my last time out of the tunnel," Barnes said in a news release. "I want to thank the Penn State family for being with me through the rough times. They're the best fans in the nation. I'm going to miss playing in front of 107,000.
"I talked with my family and we believe it's best for me to move forward and forgo my fifth year. I want to thank the fans one more time and I want to thank Penn State for the opportunity you've given me. This has been the best four years of my life. I love y'all so much."
Penn State coach James Franklin also lauded Barnes' contributions to the Nittany Lions program.
"Our staff wants to thank Deion for all he's done here at Penn State and we wish him all the best in the NFL," Franklin said. "Deion has been great contributor for us on the field and earned his degree earlier this month. We're excited to watch him take the next step."
The Nittany Lions (7-6) beat Boston College in the Pinstripe Bowl last week.