The four-year deal was done Friday, before Vikings rookie minicamp began. They have three of their eight draft picks left unsigned: first-round cornerback Mike Hughes, fourth-round defensive end Jalyn Holmes, and fifth-round tight end Tyler Conklin.
O'Neill was the 62nd overall selection, a 6-foot-6, 305-pound converted tight end. He played in all 38 games over the last three seasons for the Panthers, forgoing his final year of eligibility to enter the draft. The Vikings lauded his athleticism but stressed the need for him to add strength. O'Neill is likely headed for a backup role this season behind starting tackles Riley Reiff and Mike Remmers.