In his freshman season at Arizona State, Lockett was named to the Pac-10 All-Freshman team. In 33 games, he averaged 6.7 points and 3.4 rebounds in 19.6 minutes per game. In his sophomore season, he earned second-team All-Pac-10 honors and first-team Pac-10 All-Academic honors. In 29 games, he averaged 13.4 points, 5.3 rebounds and 2.5 assists in 30.7 minutes per game. In his junior season, he was a Capital One Academic All-District 8 honoree and was named first team all-academic by the league as well. In 25 games, he led the team in scoring and rebounding, and added 2.2 assists and 1.5 steals in 34.9 minutes per game. That season, Lockett learned his mother had cancer, and looked into playing closer to his home in Minnesota. He graduated after the season, allowing him to use his remaining year of eligibility at another school without needing to sit out a season for transferring. In 2012, Lockett transferred to Marquette for his senior year to be closer to his mother, who was suffering from lymphoma. He was named to the 2012–13 Big East All-Academic Team and was also named Marquette's Defensive Player of the Year at the season's end. In 35 games, he averaged 7.0 points, 5.1 rebounds, 1.8 assists in 26.6 minutes per game.
After going undrafted in the 2013 NBA draft, Lockett joined the Sacramento Kings for the 2013 NBA Summer League. On August 28, 2013, he signed with the Kings. However, he was later waived by the Kings on October 24, 2013. In November 2013, Lockett was acquired by the Reno Bighorns as an affiliate player. In 46 games played for the Bighorns, he averaged 11 points, 5.5 rebounds and 2 assists per game, while shooting 42.3 percent from three-point range.
On August 9, 2016, Lockett signed a one-year deal, with an option for another one, with Spanish club Real Betis Energía Plus. On December 11, 2016, Lockett recorded a career-high 27 points, shooting 9-of-16 from the field, along with seven rebounds and four steals in a 94–88 win over Joventut Badalona. In 31 games played for Betis, he averaged 11.2 points, 5.3 rebounds and 1.4 assists per game, while shooting 39.3 percent from three-point range.
In July 2017, Lockett joined the Atlanta Hawks for the 2017 NBA Summer League. On July 10, 2017, Lockett joined UNICS of the VTB United League and the EuroCup, signing a one-year deal with an option for another one. In his second season with Kazan, he helped the team reach the EuroCup Semifinals, where they eventually were eliminated by Valencia.