Arenas attended Grant High School in the Valley Glen district of Los Angeles, and accepted a scholarship offer to the University of Arizona late in his junior year.

Arenas was raised in the San Fernando Valley section of Los Angeles where he played basketball at Ulysses S. Grant High School.

He scored 10 points, grabbing 4 rebounds and dishing 4 assists, shooting 4-17 from the field and 4-13 from 3, in what would be his final game with Arizona.

In 2002–03, his sophomore season, Arenas received the NBA Most Improved Player Award averaging 18.3 points, 6.3 assists and 4.7 rebounds as Golden State improved its victory total to 38, up from 21 last season with Arenas leading the charge, and was named Most Valuable Player of the Rookie-Sophomore game during the NBA All-Star Weekend.

[13] Arenas had one of the best performances of his career during March 2003, when he dropped 41 points, grabbed six rebounds and dished five assists in a win against the Wizards which would be the team that made him their franchise player after the Warriors were unable to match.

If Arenas had been drafted in the first round, the salary cap had exceptions that would have allowed the Warriors to match the offer sheet.

The "Gilbert Arenas Rule" was later created to allow teams to re-sign restricted free agents who were not first-round picks.

[17] Arenas battled a strained abdominal muscle injury all season which would cause him to have only to start 52 games in his first year in Washington and constantly sitting on the sidelines dropped his shooting percentage instead of breaking out into the franchise cornerstones in his first year Washington envisioned, Arenas still lead the team in PPG and APG.

With Arenas being healthy, he teamed up with former teammate guard Larry Hughes (22.0 points per game) in 2004–05 to give the Wizards the highest-scoring backcourt duo in the NBA.

In the fifth game of the first round of the Eastern Conference playoffs in 2005, Arenas hit a 16-foot fadeaway as time expired to give the Wizards a 112–110 win over the Chicago Bulls.

During the off-season, Arenas said that he was willing to take a pay cut in order to give the Wizards additional money with which to sign available free agents.

One of Arenas' most memorable plays was a 40-foot jump shot in Round 1 of the 2006 NBA playoffs in which the Wizards were eliminated by the LeBron James-led Cleveland Cavaliers in six games.

Arenas himself has noted that he withdrew from the United States national team for the 2006 FIBA World Championship because he felt that assistant coaches Mike D'Antoni and Nate McMillan had determined the roster even prior to tryouts.

[citation needed] Afterward, he stated that he planned on averaging 50 points against their respective teams (Phoenix Suns and Portland Trail Blazers).

[22] Two weeks later on Martin Luther King Jr. Day he hit another buzzer-beating three-pointer to beat the Utah Jazz, 114–111, in a thriller at the Verizon Center.

[25] Towards the end of the season, Arenas tore his MCL during a game against the Charlotte Bobcats, when Gerald Wallace fell into his leg.

During the off-season, Arenas told The Washington Post that he would opt out of his contract after the 2007–08 season, making him a free agent.

"[26] Arenas only played eight games during the 2007–08 season, due to a knee injury, before he started practicing again in March, and returned to action on April 2, 2008, against the Milwaukee Bucks,[27] scoring 17 points in a 110–109 home loss.

[27] On June 9, 2008, Arenas officially opted out of the final year of his contract, but said that he would re-sign with the Wizards if they retained teammate Antawn Jamison, also a free agent.

[35] Due to the lingering injuries from April 2007, Arenas would not make his season debut until March 28, 2009, scoring 15 points and dishing 10 assists in a 98–96 loss to the Detroit Pistons.

[36] He also played a second and final game against the number one seed Cleveland Cavaliers on April 2, in which both teams wore their respective throwback jerseys.

However, Arenas' performance would be inconsistent in the weeks ahead; on November 11, he set a Wizards team record for turnovers in a game with 12.

[39] On January 1, 2010, it was also reported that Arenas and teammate Javaris Crittenton had drawn guns on each other in the Wizards' locker room during a Christmas Eve argument regarding gambling debts.

The D.C. Metropolitan Police and the U.S. Attorney's office began investigating,[40] and on January 14, 2010, Arenas was charged with carrying a pistol without a license, a violation of Washington, D.C.'s gun-control laws.

By nearly all accounts, the league felt compelled to act when Arenas' teammates surrounded him during pregame introductions prior to a game with the Philadelphia 76ers, and he pretended to shoot them with guns made from his fingers.

[45] On February 2, 2010, Arenas wrote an open editorial in The Washington Post, in which he apologized for his actions, particularly for failing to be a better role model to young fans and for "making light of a serious situation.

[48] The punishment for Arenas was significantly stiffer than for Crittenton, who received a year of unsupervised probation, or Delonte West, who had been driving around in a three-wheeled motorcycle in Prince George's County with several loaded guns including a shotgun in a violin case.

[55] In the summer of 2011, Arenas acted with former Wizards teammate Etan Thomas in a dramatic production of Our Town by Thornton Wilder.

[59] In 2023, he launched another podcast called Gil's Arena in partnership with Underdog Fantasy Sports which he hosted with Josiah Johnson and featured former NBA and WNBA players such as Brandon Jennings, Rashad McCants, Kenyon Martin, Lexie Brown and Sheryl Swoopes, with Norris Cole being a frequent guest on the show.

[citation needed] Arenas admitted that he ran about 60 red lights in 4 months and got away with it by keeping his dealer plates on his vehicle.