"I feel like I'm leaving with a bang," said James, less than a week after he helped the Ducks to a victory over Wisconsin in the Rose Bowl.
A 5-foot-9, 195-pound All-American, James rushed for a school-record 1,805 yards this season despite missing two games with a dislocated right elbow. He led the nation with an average of 150.4 yards rushing per game.
James is Oregon's career leader in yards rushing with 5,082. He is the first Pac-12 player to have three straight 1,500-yard seasons.
In Oregon's 45-38 Rose Bowl Game presented by Vizio victory over the Badgers, James rushed for 159 yards and a touchdown.
At a news conference Friday afternoon, James said he's been told he's likely a third-round pick. He hopes to improve his status with workouts.
James has his agent and training plans in order, sources told ESPN's Joe Schad on Friday.
James is one term away from completing a degree in general social science, or sociology. He may take the winter term off to train before returning to school in the spring to finish up.
He said he ultimately reached his decision on Thursday, which was difficult because of his close relationship with Oregon running backs coach Gary Campbell.
"He is a very special person and certainly will be remembered as one of the very best players ever to wear a uniform at the University of Oregon," coach Chip Kelly said in a statement released by the school. "I could not have asked any more from him and I am confident he will be a success at the next level."
Earlier this season, Stanford coach David Shaw raved about James.
"He's not a big guy, but he breaks tackles. He can stop and start. He's got some Reggie Bush characteristics at times," Shaw said. "And by all accounts, outside of playing us, I'd pull for him because he's a great kid. Everybody that I've ever had contact with who has had contact with this kid says he's a great kid."
James got off to a slow start this season with 54 yards rushing in the season-opening loss to LSU before he had 67 against Nevada, spurring talk that perhaps some weight he added in the offseason was slowing him down.
But then he reeled off three straight games with 200 or more yards.
James first grabbed attention as a redshirt freshman after running back LeGarrette Blount was suspended for punching a Boise State player after Oregon's 2009 season opener. James ran for a Pac-10 freshman-record 1,546 yards and was honored as the league's freshman of the year.
Last season he keyed the Ducks' super-fast spread offense to a 12-0 regular-season record and a berth in the BCS championship game. James declared he was returning to Oregon even before the loss to Auburn in the title game, saying he wanted to complete his education.
James leaves Oregon with several school records, including most career touchdowns (58), most career 100-yard rushing games (26) and most career points (348). He has seven career 200-yard games.
He is the eighth Ducks player to leave school for the draft with eligibility remaining.
Information from ESPN college football reporter Joe Schad and The Associated Press was used in this report.