The Charlotte native was a stud on the defensive side of the ball for South Mecklenburg High School where was a two-time All-SoMeck 8 Conference selection, a Second-Team All-Charlotte Observer squad member, on top of a local publication naming him their Defensive Player of the Year in the area. As a senior, Brannon totaled 56 tackles, six for a loss, one sack, eight interceptions, and 13 pass breakups. As a junior, he originally set the school record for interceptions in a single season with another eight, giving him 16 takeaways in his final two seasons at South Meck.
Brannon did not redshirt in his first year with the Catamounts.