Entering the NBA straight out of high school, Smith played nine seasons with the Atlanta Hawks, for the Detroit Pistons, Houston Rockets and Los Angeles Clippers between 2013 and 2016.

During the summer before his senior year, he played alongside future NBA players Randolph Morris and Dwight Howard on the Atlanta Celtics AAU team.

He averaged 22 points, 8 rebounds, 4 assists, 6 blocks, and 3 steals per game on the season, helping lead Oak Hill to 38–0 record.

[8] He became only the fifth player to record three perfect scores in the same contest along with Jason Richardson, Vince Carter, Spud Webb, and Michael Jordan.

[11] On April 28, 2008, in Game 4 of their first round series, Smith set playoff career highs of 28 points and 7 blocks in a 97–92 upset victory over the top-seeded Boston Celtics.

[14][15][16] On February 2, 2010, in a 99–106 loss to the Oklahoma City Thunder, Smith became the youngest player (at 24 years old) to record 1,000 career blocked shots.

In just under 32 minutes of action off the bench, he recorded 21 points, 8 rebounds and 3 assists in the Rockets' 117–111 overtime win over the Memphis Grizzlies.

After a blowout loss to the New Orleans Pelicans, Smith was moved back to the bench in order to help him get more comfortable with the team.

In Game 2 of the first round against the Dallas Mavericks, Smith tied his playoff career-high of 9 assists, 6 of which were alley-oops to childhood friend and former AAU teammate Dwight Howard, as he helped lead the Rockets to victory.

[31][32] He made his debut for the Clippers in the team's season opener against the Sacramento Kings on October 28, recording 1 point, 6 rebounds and 4 blocks off the bench in a 111–104 win.

[34] He made his return game for the Rockets later that night, recording 2 points (on 1-of-10 shooting), 5 rebounds, 6 assists, 2 steals and 3 blocks in a 102–98 win over the Milwaukee Bucks.

[40] On September 28, 2017, Smith joined the Israeli team Maccabi Haifa for their preseason U.S. tour, with the aim being to play in the NBA again.