In the playoffs, the Cavaliers swept the Pistons in the first round of the 2009 NBA Playoffs. James averaged 32.0 points, 11.3 rebounds and 7.5 assists in the series and became just the third player in NBA history to average at least 30 points, 10 rebounds and seven assists in a postseason series. At the end of the last game, in which he tallied 36 points, 13 rebounds and 8 assists on 16-17 free throw shooting, there were MVP chants for him in The Palace of Auburn Hills. In the next series, James once again led his team to a sweep against the Hawks. On May 22, during Game 2 of the Eastern Conference Finals, James attempted and successfully made a game winning three-point shot over Türkoglu, giving the Cavs a 96–95 victory to tie the series 1–1. Following losses in both games 3 and 4, James and the rest of the Cavs scored a victory in Game 5, making it 3–2, to send the series back to Orlando. In Game 6, he scored a playoff low 25 points and the Cavaliers lost the series to Orlando.

After a win on March 25 against the New Jersey Nets the Cleveland Cavaliers improved their record to 58–13 exceeding their previous franchise best of 57–25 set in the 1988-89 and 1991-92 NBA seasons. They ended the regular season with a league best of 66-16 after losing their final home game to the Philadelphia 76ers in overtime. The Cavaliers had a chance to tie the 1985-86 Boston Celtics for the all-time best NBA home record but ended at 39-2 after home losses to the Los Angeles Lakers and 76ers. On May 4, he was announced as the NBA Most Valuable Player. He became the youngest player as well as the first Cavaliers player in history to win the award. He was also named to the NBA All-Defensive Team for the first time in his career.

In the 2008-09 season James continued to improve facets of his game while setting new career highs. He had 23 chase-down blocks (93 blocks in total, a career-high) and improved his free-throw shooting (78.0%, a career-high, with league-leading 594 free-throws made). He was the NBA Player of the Month four times, making him the second player in NBA history to do that after Kevin Garnett did so in his 2003-04 MVP season. In addition, he became the fourth player in NBA history to lead his team in all five major statistical categories (total points, rebounds, assists, steals and blocks) in one season.

James had propelled Cleveland to a 45–37 record, good for the 4th seed in the Eastern Conference Playoffs. Prior to Cleveland's first-round series versus the Washington Wizards, Wizards guard Deshawn Stevenson said James was "overrated," prompting James to say that he would not return the insult, as that would be "almost like Jay-Z [responding to a negative comment] made by Soulja Boy." James would later say that he meant no disrespect to Soulja Boy with his comment, and that his young son is a big fan of the rapper. Jay-Z responded by producing a freestyle version of the Too Short single "Blow the Whistle", in which he "disses" Stevenson and Soulja Boy on James' behalf. The Cavaliers would go on and win the series in 6 games (4–2), setting up a meeting with the Boston Celtics. The series was decided by the seventh game in Boston. James and opponent Paul Pierce each scored 40+ points, but the Cavaliers could not get a victory, thus losing the series (4–3).

On February 27, 2008, against the Boston Celtics, James became the youngest person to score 10,000 points in his career at 23 years and 59 days, achieving the feat in style with a slam-dunk over 11-time All-Star Kevin Garnett, eclipsing the old mark by more than a year. James did so in 368 games, the ninth fastest in league history. On March 3, 2008 James was named the Eastern Conference Player of the Month for February 2008. It was the second straight month that he won the award. On March 5, 2008, James scored 50 points with 8 rebounds and 10 assists on the New York Knicks, becoming only the third player since the NBA-ABA merger to record a 50-point 10-assist game. On March 21, 2008, James scored 29 points against the Toronto Raptors, taking him past Brad Daugherty's all-time Cavaliers scoring record of 10,389 points. Daugherty achieved this record over the course of 548 games, while James took only 380 games to score 10,414 points.

In the 2007–08 season, James continued his dominant play, earning his fourth consecutive All-Star Game appearance. James was named the Eastern Conference Player of the Month for January 2008. He won the 2008 All-Star Game MVP with 27 points, 8 rebounds, 9 assists, 2 blocks and 2 steals as the Eastern Conference All-Stars defeated their Western counterparts, 134–128. On February 19, 2008, James recorded his fifth triple double of the 2007–08 season by putting up 26 points, 13 rebounds and 11 assists against the Houston Rockets. It was the 15th triple double of his career, another Cavaliers' record. He is the third youngest player to post 15 triple doubles, behind Oscar Robertson and Magic Johnson. He scored his 6th triple double of the season and 16th of his career against the Indiana Pacers the very next game. It was the second time this season that he had triple double in back-to-back games. The last player to accomplish that feat was Magic Johnson in 1988.

In the 2007 NBA Finals, James averaged 22.0 points, 7.0 rebounds and 6.8 assists, as the Cavaliers were swept by the San Antonio Spurs in four games. For the postseason, James averaged 25.1 points, 8.0 assists and 8.1 rebounds per game. He set a franchise record for double-doubles in a playoff season with eight and became the first Cavalier and the first non-guard in NBA history to have at least seven assists in eight consecutive playoff games.

In the first round of the 2007 Playoffs, James led the Cavaliers to their first sweep in franchise history over the Washington Wizards. For the series, James averaged 27.8 points, 7.5 assists, and 8.5 rebounds. In the second round of the playoffs, James led the Cavaliers to a 4–2 series victory over the New Jersey Nets. The Cavaliers advanced to the Eastern Conference Finals for the first time in 15 years. In the Eastern Conference Finals, James led the Cavaliers from an 0–2 deficit against the Detroit Pistons to win the series in six games. His performance in Game 5 was especially memorable. James recorded a franchise-record 48 points on 54.5% field goal shooting, 9 rebounds and 7 assists. In addition, James scored 29 of Cleveland's last 30 points, including the team's final 25 points in a double-overtime victory. NBA analyst Marv Albert referred to James's performance as "one of the greatest moments in postseason history," while color commentator Steve Kerr called it "Jordan-esque."

James was elected to his third consecutive All-Star game appearance during the 2006–07 season. He played a game high 32 minutes and finished with 28 points, 6 rebounds, and 6 assists. In the regular season, the Cavaliers tied the previous season's record with 50 wins and clinched the second seed of the Eastern Conference on the last day of the season. For the season, James averaged 27.3 points, 6.7 rebounds, 6.0 assists, and 1.6 steals per game. He joined Oscar Robertson as the only players in NBA history to average 27 points, 6 rebounds and 6 assists for three consecutive years.

In the 2005–06 season, James was elected to his second straight All-Star Game appearance and led the Eastern All-Stars to a 122–120 victory, with 29 points, 6 rebounds, and 2 assists. He became the youngest All-Star MVP at 21 years, 51 days. He scored 35 or more points in nine consecutive games and joined Michael Jordan and Kobe Bryant as the only players since 1970 to accomplish the feat. For the season, James averaged 31.4 points, 7.0 rebounds, and 6.6 assists per game,[10] and became the youngest player in NBA history to average at least 30 points. He also became the fourth player in NBA history to average more than 30 points, 7 rebounds and 6 assists in a single season. The Cavaliers made the playoffs for the first time since 1998, and improved from a record of 17–65 in 2002–03 to 50–32 in 2005–06.

In the 2004–05 season, James was selected to his first NBA All-Star Game and recorded 13 points, 6 assists, and 8 rebounds, as the Eastern All-Stars defeated the Western All-Stars 125–115. During the season, James became the youngest player in league history to record a triple-double, score 50 points in a game, and make the All-NBA Team. He averaged 27.2 points, 7.2 assists, 7.4 rebounds, and 2.2 steals per game. However, the Cavaliers failed to reach the playoffs again and finished with a 42–40 regular season record.

James was selected by the Cleveland Cavaliers with the first overall pick in the 2003 NBA Draft. Facing the Sacramento Kings in his first NBA game, James recorded 25 points, 9 assists, 6 rebounds, and 6 steals and shot 60% from the floor. After recording a season-high 41 points against the New Jersey Nets, James became the youngest player in league history to score at least 40 points in a game. He averaged 20.9 points, 5.9 assists, and 5.5 rebounds per game for the season, and was named 2003-04 NBA Rookie of the Year; becoming the first Cavalier and youngest NBA player to ever receive the award. He joined Oscar Robertson and Michael Jordan as the only three players in NBA history to average at least 20 points, 5 rebounds, and 5 assists per game in their rookie season.The Cavaliers improved by 18 wins and concluded the regular season with a 35–47 record, but failed to make the playoffs.

Named the consensus 2003 National High School Player of the Year…named the PARADE High School Boys Basketball Player of the Year as a junior and senior, becoming the first repeat winner in the 47-year history of the award…named the USA Today and Gatorade Player of the Year as both a junior and senior…led St. Vincent-St. Mary (SVSM) to three state championships in four seasons…named Mr. Basketball for the state of Ohio by the Associated Press (AP) for three straight seasons beginning with his sophomore year…named to USA Today All-USA First Team for three consecutive seasons beginning with his sophomore season…totaled 2,657 points, 892 rebounds and 523 assists in four seasons at SVSM.

After his rookie season, James played on the 2004 U.S. Olympic basketball team in Athens, where the United States won the bronze medal in men's basketball. It was the first time a U.S. Olympic team with NBA players failed to win the gold medal. James also competed in the 2006 FIBA World Championship in Japan and averaged 13.9 points, 4.8 rebounds, and 4.1 assists per game. However, the team finished with an 8–1 record, and was again awarded the bronze medal. James was named as one of three captains for the U.S. men's basketball national team from 2006–2008, alongside Carmelo Anthony and Dwyane Wade. After failing to win the 2006 World Championships, the team competed at the 2007 Tournament of Americas Olympic qualifiers to qualify for the 2008 Summer Olympics in Beijing. He averaged 18.1 points (on tournament-high field-goal percentage (76%) and three-point percentage (62.2%)), 4.7 assists, 3.6 rebounds and 1.5 steals in 22.2 minutes per game.