[3] Marion lettered three years in basketball, and during his high school career he earned All-Region and District honors and was nominated as a McDonald's All-American.

He was selected to the NBA All-Rookie Second Team and in 51 games (38 starts), he averaged 10.2 points, 6.5 rebounds, 1.4 assists, 1.0 blocks, 0.8 steals and 24.7 minutes.

He played for the Sophomores in the Rookie Challenge during the NBA All-Star Weekend and finished with 18 points, 3 rebounds, 2 assists, 2 steals and 1 block in 24 minutes.

In 2004–05, Marion started all 81 games for the Suns in which he appeared and averaged 19.4 points (.476 FG%, .833 FT%), 11.3 rebounds, 2.01 steals, 1.9 assists, 1.47 blocks and 38.8 minutes.

[9] In 2005–06, Marion started each of the 81 games he appeared in for the Suns and averaged 21.8 points (.525 FG%, .809 FT%), 11.8 rebounds, 1.98 steals, 1.8 assists, 1.69 blocks and 40.3 minutes.

[3] He was joined by Kevin Garnett, Elton Brand and Yao Ming as the only players in the NBA to average at least 20 points and 10 rebounds in the 2005–06 season.

[6] He also became the first Sun since Barkley to record a 30-point/20-rebound game with 31 points and an NBA season-high (and personal career-high) 24 rebounds against the Charlotte Bobcats on February 25.

During the summer, Marion had reportedly prevented a three-team deal that would have sent him to Boston with an extension, Garnett to Phoenix, and draft picks to Minnesota.

[12] On March 8, 2008, he participated in the first replayed NBA game since 1982, as the Heat played the Atlanta Hawks to settle a disputed last 51.9 seconds from their encounter on December 19, 2007.

[13] On February 13, 2009, Marion and Banks were traded to the Toronto Raptors in exchange for Jermaine O'Neal and Jamario Moon.

[17] Having been a starter his whole career, Marion was relegated to a bench role for the 2010–11 season, with Caron Butler taking over the starting small forward position.

[18] During the season, Marion joined Hakeem Olajuwon, Karl Malone, Kevin Garnett and Julius Erving as the only players with 1,500 steals and 1,000 blocks.

[6] He joined Hakeem Olajuwon, Karl Malone and Kevin Garnett as the only players in NBA history with at least 16,000 points, 9,000 rebounds, 1,500 steals and 1,000 blocks.

[6] On March 6, 2013, against the Houston Rockets, Marion passed Rod Strickland for 25th place on the NBA's all-time steals list.

[22][23] On January 3, 2014, against the Los Angeles Clippers, Marion passed the 17,000-point mark and joined Olajuwon, Malone and Garnett as the only players with at least 17,000 points, 9,000 rebounds, 1,500 steals and 1,000 blocks.

[29] Marion returned to the NBA Finals in June 2015; however, he did not appear in any of the Cavaliers' six games, a series Cleveland lost 4–2 to the Golden State Warriors.

[33] In 2017, Marion teamed up with fellow retired NBA player Cedric Ceballos to compete in Season 30 of The Amazing Race.