Marcus Sinclair Harris (born 21 July 1992) is an Australian cricketer who has represented Australia in Test cricket. A left-handed opening batter, Harris plays for Victoria and Lancashire in domestic cricket. He made his Test debut for the Australia national cricket team in December 2018 against India. He was a member of the Australian team that won the 2023 ICC World Test Championship final.

Harris began playing first-class cricket for Western Australia in the 2010–11 summer. His maiden first-class century came in just his third match, when he made 157 against Queensland. This made him the youngest Australian to score a first class 150, breaking a 115-year-old record set by Clem Hill. Harris played semi-regularly for Western Australia over the next six years, and was even named man of the match in the 2014–15 Sheffield Shield final for scoring 81 and 158 in his two innings. Harris played more than 40 Sheffield Shield matches for Western Australia and scored more than 2,000 runs for the team, but he'd only kept a batting average of 28.43 and scored just four centuries in that time. Harris also played for the Twenty20 team the Perth Scorchers, playing 14 Big Bash League (BBL) matches to score 192 runs at an average of 19.41.

Harris had a particularly poor 2015–16 season. In the Sheffield Shield he had mixed results, scoring a century but only totaling 274 runs at an average of 27.40, and his BBL form was woeful with just 69 runs from 6 innings. His performances for the Western Australian teams frustrated coach Justin Langer, who said he was "mediocre with flashes of brilliance". In Australia's national List A competition, the Matador BBQs One-Day Cup, Harris wasn't even chosen to be in Western Australia's team at all. He was instead picked up by the young Cricket Australia XI. At the end of the season Harris left Western Australia to play for Victoria.

The move to Victoria proved to be very successful for Harris. In December 2016 he was the leading run-scorer in the 2016–17 Sheffield Shield season with 409 runs at an average of 68.16. Victoria made the Sheffield Shield final, in which Harris scored a century and was part of a Shield final record-breaking opening partnership of 224 runs with Travis Dean on the first day. Harris credited his newfound form with the move to Victoria, saying that the Victorian system suited him better and it was useful to have more experienced players around him than he had had in Western Australia.

In the absence of Steve Smith, David Warner and Cameron Bancroft from the Australian Test team following the 2018 ball-tampering scandal, Harris gained his first opportunity to play Test cricket for Australia. In a Sheffield Shield match against New South Wales in October 2018, Harris helped Victoria to recover from a poor start of 2/6 with an unbeaten 250, the best score of his first-class career. This innings put him into contention for one of the vacant spots at the top of Australia's batting order. In the first four matches of the Sheffield Shield season, he scored a further two half-centuries and averaged 87.40. After 25 first-class matches for Victoria, Harris had scored five centuries and averaged 47.58, and as a result of his improved consistency he was selected in Australia's Test squad for the first time.

On the 23 March 2019, Harris became the 49th man to achieve the rare milestone of scoring 1,000 shield runs in a season. He was the seventh Victorian to achieve this feat joining Chris Rogers, Matthew Elliott, Bill Ponsford, Graham Yallop, Dean Jones and David Hussey.

The left-hander went on to make a sublime 141 off 229 balls in the 2018–2019 Sheffield Shield final which was his third century from three Sheffield Shield finals. Victoria beat New South Wales by 177 runs to win their 32nd title and Harris was named Player of the Match.

Harris finished the 2018–2019 Sheffield Shield season as the competition's leading run scorer with a total of 1,188 runs at 69.88. He was awarded the Bill Lawry Medal as Victoria's best Sheffield Shield player and was also presented the John Scholes Award for exhibiting the best Victorian values.