Junior The
Omaha Lancers of the
United States Hockey League (USHL) selected Robertson in Phase I of the 2015 USHL draft, but he instead committed to begin his
junior ice hockey career with the
Kingston Frontenacs of the
Ontario Hockey League (OHL), who drafted him in the second round, 62nd overall, of the 2015 OHL Priority Selection. He impressed head coach
Paul McFarland during rookie camp and made the Frontenacs'
2015–16 opening day roster at 16, the youngest possible age for
junior ice hockey. He recorded his first OHL goal on October 7 against the
Oshawa Generals, and on December 11, he scored his first junior
hat-trick, leading Kingston to a 4–1 victory over the
Sault Ste. Marie Greyhounds. By the OHL's Christmas break, Robertson had 16 goals for the Frontenacs, three of which came on the
power play, as well as eight assists and a +2
plus–minus rating. Those 16 goals were the most of any rookie born in 1999 by that point of the OHL season. He finished the 2015–16 season as the Frontenacs' leading rookie scorer with 18 goals and 32 points in 54 games. Those 18 goals were the most by any Kingston 16-year-old since
Anthony Stewart 14 years prior. That September, Robertson participated in the 2016
CCM/USA Hockey All-American Prospects Game at the
Wells Fargo Center in
Philadelphia, Pennsylvania. Following his breakout rookie performance, Robertson began the
2016–17 OHL season playing on Kingston's top offensive line with
Warren Foegele and Ted Nichol. While the team as a whole struggled to score at the beginning of the season, with only 21 goals through their first nine games, Robertson led the team in scoring with three goals and seven points through that same stretch. After Foegele was traded to the
Erie Otters halfway through the season, Robertson became an offensive leader for Kingston, with 26 goals and 47 points in 33 regular season games after the trade. Although the Frontenacs' 179 goals were the fewest of any OHL team during the 2016–17 season, Robertson finished with 42 goals and 81 points in 68 regular season games. Those 42 goals made up 24 percent of the Frontenacs' total scoring. He added another five goals and 18 points in 11 postseason games before the Frontenacs were swept by the
Peterborough Petes in the second round of OHL playoffs. The
NHL Central Scouting Bureau had named Robertson the No. 34 draft-eligible North American skater in their midterm rankings, but he finished the season at No. 14 overall. That June, the
Dallas Stars of the
National Hockey League (NHL) selected Robertson in the second round, 39th overall, of the
2017 NHL entry draft. After attending the Stars' 2017 training camp, Robertson returned to Kingston, where he was named one of four rotating
assistant captains for the
2017–18 season. He found strong line chemistry with
Linus Nyman at his other
wing: by November 9, both wingers had 20 goals apiece, with most of Nyman's assists coming on Robertson's goals. The Nyman—Robertson line found a
center in the second half of the season in
Gabriel Vilardi. By the halfway point of the season, Robertson led the Frontenacs with 20 goals and 42 points in 33 games. He also led the OHL with 158
shots, recording at least one shot in every game to that point. On March 7, 2018, in a 5–3 loss to the Oshawa Generals, Robertson scored his 100th career OHL goal. Robertson finished the regular season with 41 goals and a team-leading 87 points in 68 games, also becoming the first Frontenac to record 40 goals in consecutive seasons since
Mike Zigomanis in 2000 and 2001. He added another 18 points in 16 postseason games before the
Hamilton Bulldogs defeated the Frontenacs in the third round of OHL playoffs. At the end of the season, Robertson was named to the
OHL All-Star Third Team. Once the junior hockey season ended, Robertson signed a three-year
entry-level contract with the Stars, Returning to the Frontenacs as an assistant captain, Robertson began the
2018–19 season on an offensive tear: by mid-November, he led the OHL with 22 goals in as many games and was seventh in the league with 33 points. He scored 38.6 percent of the Frontenacs' 57 goals and either scored or assisted on 57.9 percent. After recording two hat-tricks in the same week, first against the
Ottawa 67's and then the Oshawa Generals, Robertson was named both the OHL On the Run Player of the Week and a
Canadian Hockey League Top Performer of the Week for the week ending November 11. On November 20, the week after receiving these accolades, Robertson and
defenseman Jacob Paquette were traded to the
Niagara IceDogs for Billy Constantinou, Ian Martin, and 11 draft picks. At the time of the trade, Robertson had 23 goals and 15 assists in 24 games. Robertson continued his offensive performance on his new team, with eight goals and 22 points for Niagara by the midseason break, and he was named the OHL Player of the Month in November after recording 12 goals and 30 points in 12 games between the two teams. With two assists in a 6–4 win over the
North Bay Battalion on March 1, Robertson recorded both his 100th point of the 2018–19 season and his 300th career OHL point. In the final week of the regular season, Robertson recorded 11 points in three games to clinch the OHL Central Division title for the IceDogs. With 48 goals and 117 points in 62 games, including 25 goals and 79 points in 38 games for Niagara, Robertson won both the 2019
Eddie Powers Memorial Trophy for the OHL's regular season scoring leader and the
CHL Top Scorer Award. Robertson closed out the 2018–19 OHL awards season with a selection to the All-Star First Team. He finished his OHL career with 149 goals and 317 points in 252 games. On February 13, 2020, following an injury to
Alexander Radulov, the Dallas Stars called Robertson up for his NHL debut. He debuted that night, recording his first NHL assist on
Tyler Seguin's goal during the Stars' 3–2 victory over the
Toronto Maple Leafs. That was his only point in his three-game call-up before he was sent back down to the AHL on February 17. By the time that the
COVID-19 pandemic suddenly halted both the NHL and AHL regular season, Robertson had 25 goals and 47 points in 60 games for the Texas Stars. Robertson was one of several young
prospects who traveled with the Stars to the
2020 Stanley Cup playoffs, but he was invited primarily to watch the team and did not play during Dallas's playoff run. A COVID-19 outbreak and several injuries postponed the start of the Dallas Stars' regular season and forced them to retool their roster. Robertson was named to the team's opening night roster as a fourth-line winger alongside
Nick Caamano and
Jason Dickinson. After playing in the first two games of the season, Robertson was demoted to Dallas's
taxi squad for a five-game stretch. He returned at the start of February, and on February 7, Robertson scored his first NHL goal when he deflected a shot from
Miro Heiskanen past
Malcolm Subban of the
Chicago Blackhawks. In the month following that goal, Robertson began producing offensively for Dallas, with three goals and eight points in his next 11 games. By April 11, Robertson's 27 points were second only to
Kirill Kaprizov's 40 among rookie scorers. He was named the
NHL Rookie of the Month in April after recording eight goals and 18 points, including at least one point in 13 of 17 games. While the Stars narrowly missed the
2021 Stanley Cup playoffs, Robertson finished the season with 17 goals and a rookie-leading 28 assists in 51 games. In addition to being named to the 2020–21
NHL All-Rookie Team, Robertson was the runner-up for the
Calder Memorial Trophy, given to the top rookie in the NHL. The award was won by Kaprizov of the
Minnesota Wild. Because Robertson was still on his entry-level contract at the time of the
2021 NHL expansion draft, he was automatically protected from being drafted by the
Seattle Kraken. during the
2023 Stanley Cup playoffs Robertson missed the first seven games of the season with a shoulder injury but returned at the end of October to continue the scoring pace he had set the previous season. Playing on the top line with
Roope Hintz and
Joe Pavelski, Robertson recorded 17 points in his first 15 games of the season. On December 2, Robertson scored on
Daniil Tarasov only 68 seconds into the Stars' game against the
Columbus Blue Jackets. It was the fourth game in a row in which Dallas had scored within the first 75 seconds of the game, an NHL record. Three months later, on March 4, 2022, Robertson recorded his first NHL hat-trick in his 100th career game, a 4–3 overtime win against the
Winnipeg Jets. He recorded another hat-trick two days later, this time during a 6–3 victory over the
Minnesota Wild. He was the first Dallas Stars player ever to record hat-tricks in consecutive games, the first NHL player under the age of 23 to do so since
Filip Forsberg in 2017, and the first of any NHL player since
Alexander Ovechkin in January 2020. Robertson finished the regular season with 41 goals and 79 points in 74 games. He scored the most goals of any player since
Jamie Benn during the season, and was only the fourth member of the Stars to reach the 40-goal mark following their relocation to Dallas. The Stars faced the
Calgary Flames in the first round of the
2022 Stanley Cup playoffs, with Robertson making his postseason debut in Game 1. He struggled in the series, with only one assist through four games, and he was moved off of the top line for Game 5. On his new line with Benn and
Tyler Seguin, Robertson scored his first postseason goal in Game 5. The Flames defeated the Stars in seven games, and Robertson finished his first playoff series with one goal and four points. On October 5, 2022, after missing training camp and a majority of the preseason, Robertson signed a four-year contract with the Stars. He made the Stars' opening roster for the
2022–23 NHL season and recorded an assist in the first game. Robertson then recorded three points in the second game of the season. In January 2023, Robertson was chosen to represent the Dallas Stars in the
2023 NHL All-Star Game, his first time being selected. ==International play==