Nixon, who announced his decision Tuesday, becomes the second Buffaloes receiver to leave early for the draft after Laviska Shenault Jr. announced his decision last week.
This marks the second time that more than one Colorado player has declared early for the NFL draft after a season. Defensive lineman Shannon Clavelle and running back Rashaan Salaam departed for the 1995 draft.
Nixon finished with 89 catches for 1,118 yards and seven touchdowns, according to ESPN Stats & Information. He ranked 25th in receptions and yards receiving in school history.
On Sunday, Nixon was given the Eddie Crowder Award at the team's banquet for outstanding team leadership.
"This University has molded me into a man and helped me both mentally and physically," Nixon said on Twitter. "I will cherish the relationships I made here no matter what and always be very proud to be part of this family. Football has opened many doors and blessings in my life."
Nixon's plan is to finish the semester in the classroom and then start training for the NFL combine.
The Associated Press contributed to this report.