Born in Pasadena, Texas, Walkup attended Deer Park High School in nearby Deer Park. He was a point guard in his junior season for the varsity basketball team and averaged 10.1 points, 5.0 blocks, 4.6 assists, and 1.9 steals per game. Walkup also earned all-district honors after helping the Deer finish the season with a 24–11 record. He also lifted them to a bi-district round victory at the Class 5A playoffs. As a senior, Walkup averaged 25.9 points and 8.9 rebounds with Deer Park. In his years with the school, he faced two ACL injuries and a broken foot. In November 2010, Walkup committed to play college basketball at Stephen F. Austin State University for the Lumberjacks. He chose the school because he aspired to compete in the NCAA Division I Tournament and they ran a successful program. Houston Baptist was the only other school that offered him a scholarship. Walkup later said, "There was a reason I didn’t have any other scholarship offers besides those two—I wasn't any good." His father commented on Walkup's recruitment, "I'm sure scouts looked at him and said, 'Well, he's a 6–4 white guy and he can't shoot and he plays the four. And we don't need that.'"
College career
Walkup immediately assumed a big role with the Lumberjacks as the team's sixth man during his freshman season. In 18.5 minutes per game, he averaged 4.4 points and 3.6 rebounds. He recorded a season-best 11 points twice, against Tulsa on November 24, 2012, and versus McNeese State on January 5, 2013. That season, the Lumberjacks won a school-record 27 games, winning their third Southland Conference title of all-time and qualifying for the National Invitation Tournament. As a junior at Stephen F. Austin, Walkup averaged 15.5 points and 6.5 rebounds per game. His teammates began referring to him as "The Snake", after establishing his ability for rebounds, consistently drawing fouls for opposing players, and providing scrappy defense for the Lumberjacks. He was named Southland Conference Player of the Year in 2015. In the first round of the 2016 NCAA Tournament, Walkup scored 33 points in a 70–56 upset over third-seeded West Virginia. He shot 19 for 20 on free throws.
Walkup was born on December 30, 1992 to Lisa and Raymond Walkup and was brought up in Pasadena, Texas. He has an older brother named Nathan who played as a forward for the Texas A&M Aggies men's basketball team from the 2007–08 season to 2010–11 season. Both players graduated at Deer Park High School and played under Coach Louis Means. Walkup has often been known for his beard, which drew the attention of several media outlets during the 2016 NCAA Tournament. Entering that year's tournament, he had not shaved since November 1, 2015. Walkup claimed that he had been asked to shave it, but he felt that it fit in with Stephen F. Austin's mascot, the Lumberjacks. His appearance has also been compared with Philadelphia Philliesbaseball playerBryce Harper. He has also been nicknamed "Fresh Cut" by Barry Knight.
