Benjamin Marshall is a New Zealand professional rugby league coach and former player who is the head coach of the Wests Tigers in the NRL. He played at five-eighth or halfback for the Wests Tigers in two separate spells, St. George Illawarra Dragons, Brisbane Broncos and South Sydney Rabbitohs in the National Rugby League (NRL), and at representative level for the NRL All Stars and New Zealand Kiwis. Marshall was also briefly a professional rugby union player with the Blues in Super Rugby.

Marshall was born in Whakatane, New Zealand. He is of Maori descent. He is the eldest of three brothers, and the elder brother of New Zealand Maori international Jeremy Marshall-King. He was raised without his biological father, but has spoken of the influence of his foster-father Michael Doherty. Marshall was a pupil at Whakatane High School. He was offered a scholarship to play for Keebra Park State High School in Gold Coast, Queensland when he was 16. While living on the Gold Coast, he played junior rugby league for the Nerang Roosters. While in high school in Australia, Marshall played for the Australian Schoolboys team in 2003.

In Round 20 of the 2003 NRL season, Marshall made his NRL debut for the Wests Tigers against the Newcastle Knights, coming on as a replacement in the 14th minute as fullback. Marshall continued to make appearances for Wests Tigers for the remainder of 2003 when his studies allowed, playing halfback. In Round 24 against the Penrith Panthers, Marshall scored his first NRL try in the Tigers 44–28 loss at Penrith Stadium.

In 2005, Marshall injured his other shoulder in the opening minutes of the first trial match. After missing the opening round match, Marshall played five-eighth for the club's second match of the year against defending premiers, the Bulldogs. With an injury free run, Marshall demonstrated a passing, running, and kicking game to complement his stepping. He was able to score individual tries and set up tries for his team-mates. Marshall also made his New Zealand debut in the 2005 ANZAC Test. Marshall was a member of the Wests Tigers that defeated North Queensland Cowboys in the 2005 NRL grand final, where he famously set up a 90-metre try to Pat Richards, which was considered to be one of the best tries of grand final history.

A shoulder injury would marr 2006, before producing dominant performances for the Tigers, but eight weeks into his come-back in 2007 he dislocated the same shoulder that had been dislocated against North Queensland, and he missed the rest of the season. 2008 Marshall's injury troubles continued when he suffered a knee ligament tear in the third minute of the season's opening game. Marshall was named in the 24-man Kiwis squad for the NZ Kiwi's. He captained New Zealand for the first time on 8 November, Marshall scored a try and kicked two conversions in the World Cup final victory over the Kangaroos. It was the Kiwis first ever World Cup victory, in a game they were considered "massive underdogs."

In March, despite speculation that he might play rugby union in Japan, Marshall signed with the Wests Tigers for a further two seasons through to the end of 2011. Following Kiwis captain Nathan Cayless' retirement from international football, Marshall was named as captain in that year's ANZAC test. Marshall returned to his old position of five-eighth from July, though both Marshall and coach Tim Sheens insisted that Marshall had been switching between first and second receiver throughout the entire season.

In March 2010, Marshall scored two tries against the Eels to become the highest try-scorer for the Wests Tigers, breaking the record of 43 previously held by Daniel Fitzhenry. He played in 34 games in 2010, the most of any NRL player, including the Tigers' 13–12 loss in the preliminary final to the Dragons.

In round 14 of the 2011 season, Marshall scored 2 tries against the New Zealand Warriors. He had then scored a try against every team in the NRL. Before the end of the season he had eclipsed Brett Hodgson as the highest scorer in the short history of the Wests Tigers, having amassed 797 points in 151 games. Marshall was the top point-scorer for the 2011 NRL season, winning the Dally M Five-Eighth of the Year and also placing second in the Dally M Player of the Year voting.

Marshall captained the NRL All Stars team to victory in the inaugural 2012 Arthur Beetson trophy. He was one of the few players to appear in every Wests Tigers game for the year and, despite the club's poor showing, led the NRL in try assists and line-break assists in the regular season. In the penultimate game of the regular season, Marshall kicked two goals to become the first Wests Tigers and 43rd player in the Australian competition to score one thousand points. At the end of the season he was nominated for the Dally M halfback of the year.

In July 2013, Marshall sought a release from the remaining two years of his contract with Wests Tigers to pursue a career in rugby union, after the club declined to offer him a contract extension and upgrade that had been previously verbally agreed upon. Marshall signed a two-year deal with the Auckland Blues franchise worth close to $500,000 a season. In May 2014, Marshall signed a 2+1⁄2-year contract with the St George Illawarra Dragons. He finished the year playing in 15 games and scoring 3 tries. In 2015, Marshall steered the Dragons to their first NRL finals series since coach Wayne Bennett left the club at the end of the 2011 season.

In 2017, after rejecting a one-year extension worth $300,000, Marshall decided to reunite with Wayne Bennett and sign with the Brisbane Broncos on a one-year deal. In 2018, Marshall signed a deal in August 2017 to go back to his first club The Wests Tigers for one year. In 29 January 2021, Marshall signed a one-year contract with the South Sydney Rabbitohs. Marshall played a total of 22 games for South Sydney in the 2021 NRL season including the club's 2021 NRL Grand Final defeat against Penrith. Following the NRL premiership decider, Marshall announced his retirement on 6 October.

In 2022, it was announced that Marshall would be appointed the Tigers' assistant coach under long-time head coach Tim Sheens, however due to the Tigers' poor 2023 season, the club mutually parted ways with Sheens in August, with Marshall moving into the head coach role a year earlier than expected. Marshall would assume the role in the Tigers' Round 25 match, where the Tigers would break a 10-game losing streak, defeating the Dolphins 24–22.

In August 2024 the NRL announced that Marshall was an inductee into the National Rugby League Hall of Fame. Marshall, who was ascribed Hall of Fame number 123, was amongst eleven male players in the 2024 Class.