Winslow was a four-year starter at St. John's School in Houston, Texas. He started and ended his career at St. John's with league championships. He was the 2013 Gatorade Texas Player of the Year and averaged 27.5 points, 13.6 rebounds, 3.5 assists, 2.1 blocks and 1.8 steals per game as a senior in 2013–14. Winslow was selected as a McDonald's All-American in 2014.
College career
Winslow averaged 14 points and five rebounds in his first five games in a Duke uniform. Duke coach Mike Krzyzewski compared Winslow's game to that of former Duke stars Tommy Amaker and Grant Hill. On February 9, 2015, Winslow was named ACC Freshman of the Week, and later earned honorable mention All-ACC honors. In the NCAA tournament, Winslow averaged 14.3 points and 9.3 rebounds per game en route to a national championship. He played in 39 games for Duke as a freshman, averaging 12.6 points, 6.5 rebounds, 2.1 assists and 1.3 steals in 29.1 minutes per game. In April 2015, Winslow declared for the NBA draft, forgoing his final three years of collegiate eligibility.
On June 26, 2015, Winslow was selected by the Miami Heat with the 10th overall pick, in the 2015 NBA draft. On July 3, 2015, he signed his rookie scale contract with the Heat. He made his debut for the Heat in the team's season opener against the Charlotte Hornets on October 28, recording five points and seven rebounds off the bench in a 104–94 win. On November 6, he had a then season-best game with 13 points and eight rebounds in a loss to the Indiana Pacers. On January 11, he made his first career start, recording seven points and three rebounds in a loss to the Golden State Warriors. On February 22, he recorded a season-high 15 points, seven rebounds and four assists in 39 minutes off the bench in a 101–93 win over the Indiana Pacers. On March 14, he topped his season-high mark with 20 points in a 124–119 win over the Denver Nuggets. During his rookie year, coach Erik Spoelstra consistently called on Winslow to defend the most lethal attackers in the league, from LeBron James to James Harden, as he developed into a defensive stopper. At the season's end, he earned NBA All-Rookie Second Team honors.
2016–17 season
Winslow started all nine games for the Heat to begin the season before missing the next 16 with a sore left wrist. On December 22, 2016, he had a season-best game with 23 points and 13 rebounds in a 115–107 win over the Los Angeles Lakers, as he set a career high for points and tied a career best in rebounds. On January 5, 2017, Winslow was ruled out for the rest of the season after undergoing surgery to repair a torn labrum in his right shoulder.
2017–18 season
Winslow played in all 27 games to begin the season, and scored a season-high 15 points on December 9 against the Brooklyn Nets. He then missed 14 games with a knee strain between December 15 and January 10. On February 5, he scored 16 points against the Orlando Magic. He twice scored 17 points between February 24 and March 1, before setting a season-best 18 points on April 4 against the Atlanta Hawks. On March 12, he recorded 15 points and a season-high 13 rebounds against the Portland Trail Blazers. In Game 3 of the Heat's first-round playoff series against the Philadelphia 76ers, Winslow scored a season-high 19 points in a 128–108 loss.
2018–19 season
On November 3, 2018, in his first start of the season, Winslow had 15 points, 10 rebounds and eight assists in a 123–118 loss to the Atlanta Hawks. On December 10, he scored a career-high 28 points with six 3-pointers in a 108–105 loss to the Los Angeles Lakers. After teammate and starting point guard Goran Dragić suffered a right knee injury, Winslow was named as Miami's starting point guard in mid-December. On December 28, he had 24 points, 11 rebounds and seven assists in a 118–94 win over the Cleveland Cavaliers. On January 10, he recorded a career-high 11 assists in a 115–99 win over the Boston Celtics.
Memphis Grizzlies (2020–present)
On February 6, 2020, Winslow was acquired by the Memphis Grizzlies in a three-team trade also involving the Minnesota Timberwolves. On July 21, 2020, the Memphis Grizzlies announced that Winslow had suffered a hip injury during team practice and would miss the rest of 2019–20 season.
