He enrolled at Alexander Hamilton High School, using the address of one of his mother’s friends to gain the advantages of a better academic and athletic reputation than his neighborhood high school could offer. He had little playing time until his junior year, when he took over as varsity starting quarterback. In his senior season in 1973, they reached the city playoffs, and Moon was named to the all-city team.

Moon attended two-year West Los Angeles College, and was a record-setting quarterback as a freshman in 1974, but only a handful of four-year colleges showed interest in signing him. Offensive coordinator Dick Scesniak of the University of Washington in Seattle, however, was eager to sign the rifle-armed Moon. Adamant that he play quarterback, Moon considered himself to be perhaps a slightly above-average athlete who lacked either the size, speed, or strength to play other positions.

Under new head coach Don James, Washington was 11–11 in Moon’s first two seasons as a starter, but as a senior in 1977, he led the Huskies to the Pac-8 title and a 27–20 upset win in the Rose Bowl over Michigan. Moon was named the game’s Most Valuable Player on the strength of two short touchdown runs and a third-quarter 28-yard touchdown pass to wide receiver Robert “Spider” Gaines.

Despite his collegiate success, Moon went unselected in the 12-round NFL Draft. With no takers in the NFL, he turned to the Canadian Football League. Moon signed with the Edmonton Eskimos, where he and Tom Wilkinson shared signal-calling duties and helped lead the Eskimos to a record five consecutive Grey Cup victories in 1978, 1979, 1980, 1981, and 1982. Moon won the offensive Grey Cup Most Valuable Player award in the 1980 and 1982 games, and became the first professional quarterback to pass for 5,000 yards in a season by reaching exactly 5,000 yards in 1982.

Moon married Felicia Hendricks, whom he had known since they were 16 years old, in 1981. In 1994, a former Vikings cheerleader accused Moon of sexually harassing her and the case was settled out of court. In 1995, Moon was arrested after an incident with his wife at their home. Moon was acquitted after his wife testified that she initiated violence and that he was trying to restrain her. They divorced in 2001.

Moon’s decision to enter the NFL touched off a bidding war for his services, won by the Houston Oilers, led by Hugh Campbell, his head coach for his first five seasons in Edmonton. Gifford Nielsen—the starting quarterback in 1983—retired after Moon joined the team, stating that Moon becoming the starter was inevitable. Moon had a difficult adjustment period, but threw for a franchise-record 3,338 yards in his first season in 1984, but Campbell was just 8–22 (.267) at the helm and did not finish the 1985 season. When new head coach Jerry Glanville found ways to best use Moon’s strong arm in 1986, the team began having success. In the strike-marred 1987 season, the Oilers posted a 9–6 record, their first winning season since 1980. In his first postseason game in the NFL, Moon passed for 237 yards and a touchdown in the Oilers’ 23–20 overtime win over the Seattle Seahawks in the wildcard round of the playoffs.

Prior to the 1989 season, Moon signed a five-year, $10-million contract extension, which made him the highest-paid player in the NFL at that time. In 1990, Moon led the league with 4,689 passing yards. He also led the league in attempts (584), completions (362), and touchdowns (33), and tied Dan Marino’s record with nine 300-yard games in a season. That included throwing for 527 yards against Kansas City on December 16, 1990, the second-most passing yards ever in a single game. The following year, he again led the league in passing yards, with 4,690. At the same time, he joined Marino and Dan Fouts as the only quarterbacks to post back-to-back 4,000-yard seasons. Moon also established new NFL records that season with 655 attempts and 404 completions.

In 1992, Moon played only 11 games due to injuries, but the Oilers still managed to achieve a 10–6 record, including a victory over the Buffalo Bills, in the final game of the season. Two weeks later, the Oilers faced the Bills again in the first round of the AFC playoffs. Aided by Moon’s 222 passing yards and four touchdowns in the first half, Houston built up a 28–3 halftime lead and increased it to 35–3 when Buffalo quarterback Frank Reich’s first pass of the third quarter was intercepted and returned for a touchdown. The Bills stormed back with five unanswered second-half touchdowns to take a 38–35 lead with time running out in the final period. Moon managed to lead the Oilers on a last-second field goal drive to tie the game at 38 and force overtime, but threw an interception in the extra period that set up Buffalo kicker Steve Christie’s game-winning field goal. The Bills’ rally from a 32-point deficit was the largest comeback victory in NFL history and is now known in NFL lore simply as the Comeback. Moon finished the game with 36 completions for 371 yards and four touchdowns, with two interceptions. His 36 completions was an NFL postseason record.

The 1993 season was the Oilers’ best with Moon, but was his last with the team. Despite a drama-filled 1–4 start and early struggles from Moon, Houston went 12–4 and won the AFC Central division crown, but lost to Joe Montana and the Kansas City Chiefs 28–20 in the divisional round of the playoffs.

Moon was traded to the Minnesota Vikings after the season, where he passed for over 4,200 yards in each of his first two seasons, but missed half of the 1996 season with a broken collarbone. The Vikings’ starting quarterback job was given to Brad Johnson and Moon was released after he refused to take a $3.8-million pay cut to serve as Johnson’s backup. Moon then signed with the Seattle Seahawks as a free agent, made the Pro Bowl, and was named Pro Bowl MVP. After a two-year stint in the Pacific Northwest, an aging Moon signed as a free agent with the Kansas City Chiefs as a backup in 1999. He played in only three games in two years with the Chiefs and announced his retirement at age 44 in January 2001. His 291st (308th, including postseason play) and final touchdown pass was an 8-yard pass to Troy Drayton against the Rams on October 22, 2000, a game in which the Chiefs defeated the defending champs, 54-34.

In his six years in the CFL, Moon amassed 1,369 completions on 2,382 attempts (57.4 completion percentage) for 21,228 yards and 144 touchdown passes. He also led his team to victory in 9 of 10 postseason games. He was inducted into the Canadian Football Hall of Fame in 2001 and the Eskimos’ Wall of Honour. In 2006, he was ranked fifth on a list of the greatest 50 CFL players presented by Canadian sports network TSN.

Moon set a franchise record with Houston for wins with 70, which stood until Steve McNair broke it in 2004, long after the team had become the Tennessee Titans. He also left the Oilers as the franchise leader in passing touchdowns, passing yards, pass attempts, and pass completions, all of which still stand today.

Moon was named to 9 Pro Bowl games (1988–1995, 1997). He works as a broadcaster for the Seattle Seahawks on both TV and radio. On radio, he is a play-by-play announcer with former Seattle Seahawks receiver Steve Raible. He was elected into the Pro Football Hall of Fame in 2006, becoming both the first Canadian Football Hall of Fame player, first undrafted quarterback, and first African-American quarterback honored; he was elected in his first year of eligibility. The Tennessee Titans retired his number at halftime on October 1, 2006 vs the Dallas Cowboys. Moon won his first Super Bowl ring in 2014 as a broadcaster for the Seattle Seahawks.

Combining his NFL and CFL stats, Moon’s numbers are nearly unmatched in professional football annals: 5,357 completions in 9,205 attempts for 70,553 yards and 435 touchdowns. Even if his Canadian Football League statistics are discounted, Moon’s NFL career numbers are still exceptional: 3,988 completions for 49,325 yards, 291 touchdown passes, 1,736 yards rushing, and 22 rushing touchdowns. Warren Moon also held individual NFL lifetime records for most fumbles recovered (56) and most fumbles made (162), but this was surpassed by Brett Favre in 2010. Moon was in the top five all-time when he retired for passing yards, passing touchdowns, pass attempts, and pass completions.

Moon has mentored Cam Newton, the first overall pick of the 2011 NFL Draft, alluding to their common experiences as prominent African-American quarterbacks. He was suspended indefinitely from his sportscaster position after he was sued, in December 2017, for sexual harassment.

In 2017, Moon was sued for sexual harassment by his former personal assistant. The case was settled in 2019.