O'Brien transferred from Maryland after two successful seasons in the ACC and was buried on the Badgers depth chart after an un-impactful season in the Big Ten last year.
He started three games for the Badgers, but a 14-3 deficit at halftime of the third game against Utah State forced then-coach Bret Bielema to replace the highly touted transfer with freshman QB Joel Stave. O'Brien played sparingly the rest of the season.
The comparisons between O'Brien and former Badgers QB Russell Wilson -- another ACC transfer -- were inevitable, but O'Brien struggled to find anywhere near the consistency that Wilson showed in his one year in Madison.
O'Brien was expected to be the fourth or fifth QB on the depth chart once camp broke this season. His chances of seeing any significant playing time this season affected his decision, the Journal Sentinel reported.
O'Brien has one year of eligibility left. He came to Wisconsin and played immediately under the same rule that allowed Wilson to transfer from NC State -- the graduate transfer exception -- but that only applies one time.
He could potentially play right away at an FCS school, such as Appalachian State, which is located in his native North Carolina.
With Wisconsin, O'Brien completed 52 of 86 passes for 523 yards along with three touchdowns. He threw one interception.
For more, follow Mike Singer on Twitter @RealMikeSinger.