Smith was born in Greenwood, Mississippi. He attended Raytown High School in Raytown, Missouri, where he played for the Raytown Bluejays high school football team. As a senior, he recorded 60 tackles, 21 tackles for loss, 12 sacks, while adding seven forced fumbles, one blocked punt, and a safety on defense, while on offense, he caught 34 passes for 570 yards and four touchdowns as a tight end.
Considered only a three-star recruit by the Rivals.com recruiting network, Smith was considered the No. 5 overall prospect (any position) in the state of Missouri as well as the No. 27 strongside defensive end in the nation. Smith chose Mizzou over Nebraska, Kansas, and Kansas State, among many others.
Smith played for the Missouri Tigers football team under head coach Gary Pinkel while attending the University of Missouri from 2008 to 2010. After being redshirted as a freshman in 2008, he started 11 of 13 games at defensive end in 2009. He finished the season with 60 tackles and 11 sacks. He was named the Big 12 Defensive Freshman of the Year and a first team freshman All-American. As a sophomore in 2010, he played in nine games, recording 48 tackles and six sacks.
After the season, Smith announced that he would forgo his final two years of eligibility and enter the 2011 NFL Draft.2009 First-team Freshman All-American (College Football News, Phil Steele)
2009 Big 12 Defensive Newcomer of the Year (Associated Press)
2009 Big 12 Defensive Freshman of the Year (Coaches)
2009 Hendricks Award Watch List
2009 Second-team All-Big 12 (Associated Press)
2009 Honorable mention All-Big 12 (Coaches)
2009 Team Defensive Lineman of the Year Award
2009 Team Freshman of the Year Award
Playing as a defensive end at Missouri, Smith was considered a "DE/OLB prospect" by most NFL scouts and was considered a strong edge run defender as 4-3 end or 3-4 linebacker. Many scouts had compared him to DeMarcus Ware. Prior to the 2011 NFL Draft, he was projected to be selected in the mid-late first round by mock draft analysis. On the day of the Draft, the San Francisco 49ers decided to draft Smith in the first round with the seventh overall pick.
Smith did not start, but did make his NFL debut against the Seattle Seahawks. In Week 4, against the Philadelphia Eagles, he recorded his first sack on Michael Vick. In the next two weeks, Smith would win the Pepsi NFL Rookie of the Week in victories against the Tampa Bay Buccaneers and Detroit Lions. After a strong October, Smith became the first 49ers player since linebacker Patrick Willis in 2007 to earn the NFL Rookie of the Month, he recorded 13 tackles, 6.5 sacks including one that forced a safety as he helped San Francisco to a 6-1 record. In Week 15, Smith recorded 2.5 sacks against the Pittsburgh Steelers. He also surpassed Charles Haley for the 49ers record for most sacks by a rookie in a single season with 13.0 sacks. He finished with 37 total tackles, four pass deflections, two forced fumbles, and 14 sacks. Smith was half a sack shy of tying the all-time rookie sack record held by defensive end Jevon Kearse despite not starting a single game in his rookie season. He was named Defensive Rookie of the Year by Pro Football Writers of America, and finished second to Von Miller for the Associated Press NFL Defensive Rookie of the Year Award
After being used only as a situational pass rusher throughout his rookie season, Aldon Smith became a full-time starter in the 2012 season. In Week 11, he recorded 5.5 sacks against the Chicago Bears. The next week, in a game against the New Orleans Saints, he surpassed Reggie White as the fastest player in league history to record his 30th career sack, doing so in 27 games. The next week, against the St. Louis Rams, Smith broke another of White's records by recording 31.5 sacks in his first two seasons. In that same game, he tied Fred Dean's franchise record of 17.5 sacks in one season. On the NFL Network's NFL Top 100 Players of 2013 ranking, the players voted him the seventh best player in the league entering the 2013 season, which made him the second highest ever debut and second highest defensive player on the list, both behind J. J. Watt. He was also voted the San Francisco 49ers MVP in 2012.
Smith got off to a fast start during the 2013 season getting 4.5 sacks in the first three games. However, on September 20, Smith was involved in a single vehicle accident in San Jose, California. He was subsequently arrested on suspicion of driving under the influence and possession of marijuana. After the loss to the Indianapolis Colts in the third week of the football season, he voluntarily entered a rehabilitation facility, to be put onto the non-football injury list with an indefinite leave of absence.
Smith missed five games in rehabilitation, he would return to the team in Week 10 against the Carolina Panthers but in a backup role, he would not start a game until Week 13 against the St. Louis Rams. He ended the season strong finishing with 34 tackles and 8.5 sacks. Smith was ranked #33 in the NFL Top 100 Players of 2014.
Smith served a nine-game suspension for violating the NFL's substance abuse and personal conduct policies. He was reinstated in Week 11.
On August 7, 2015, following an arrest for his third DUI, Smith was released by the 49ers.
On September 11, 2015, Smith signed a one-year contract with the Oakland Raiders. He collected two tackles in his first game with the Raiders in their season opening loss against the Cincinnati Bengals. He got his first start with the Raiders on September 27, against the Cleveland Browns and finished with two solo tackles. The following week, he earned his first sack against the Chicago Bears and finished the game with a season-high six tackles. He played his last game of the season on November 15 and finished the 14-30 loss with three tackles and one sack. Two days later, the NFL issued Smith a one-year suspension due to his hit-and-run on August 6, 2015. (See Legal issues) He finished his first season with the Oakland Raiders with a total of 28 tackles and three and a half sacks in seven starts and nine games.
On April 4, 2016, Smith re-signed with the Raiders. On October 27, 2016, Smith applied for reinstatment with his one-year suspension coming to an end on November 17, 2017.
On January 28, 2012, Smith was arrested for driving under the influence in Miami Beach, Florida.
On June 30, 2012, Smith was believed to have suffered stab wounds when attempting to break up a fight at a party at his residence. Two other people were shot in the incident. On October 9, 2013, Smith was charged with "three felony counts of illegal possession of an assault weapon" relating to the stabbing incident. The charges were later reduced to misdemeanors.
On September 20, 2013, Smith was involved in a single vehicle accident in San Jose, California. He was subsequently arrested on suspicion of driving under the influence and possession of marijuana. After the loss to the Indianapolis Colts in the third week of the football season, he voluntarily entered a rehabilitation facility, to be put onto the non-football injury list with an indefinite leave of absence.
On April 13, 2014, Smith was detained and arrested following an incident at the Los Angeles International Airport in which Smith became belligerent and uncooperative with a TSA agent, who alleged Smith claimed he was carrying a bomb. After interviews revealed that Smith did not clearly state he was carrying a bomb, the Los Angeles City Attorney decided to drop the charges. Smith was suspended for nine games for the 2014 season.
On August 6, 2015, Smith was arrested in Santa Clara, California, for an alleged hit and run after driving under the influence, and vandalism charges. He was released by the 49ers the next day as a result.
On March 9, 2017, Smith was a passenger with a friend driving to Smith's house at 12:00 AM, when San Francisco police department found out both Smith and the driver were under the influence. Even though Smith was not the driver, both Smith and his friend were detained by San Francisco Police Department for questioning. On March 10, Smith and his friend were released. No arrests were made.
On September 23, 2017, it was announced that Smith had agreed to plead No Contest to Hit and Run in the 2015 incident in exchange for the DUI charges being dropped. He was sentenced to 20 days in a residential treatment facility and is indefinitely forbidden from entering any bars or other establishments where alcohol is the primary commodity being sold.