A left-handed player with a one-handed backhand, Shapovalov plays an aggressive, high-risk ground game and has some of the strongest groundstrokes on the tour, complemented by his powerful forehand and serve.

[16] He started playing tennis at the Richmond Hill Country Club, where his mother got a job as a coach two weeks after arriving in Toronto from Tel Aviv.

When it became difficult to get Denis enough time on the Richmond Hill club's courts, his mother left her job there and eventually opened her tennis academy in Vaughan, named TessaTennis, to help give him a home base to train and to teach the game to other juniors.

[23] In October 2015, Shapovalov and fellow Canadians Félix Auger-Aliassime and Benjamin Sigouin captured the first Junior Davis Cup title for Canada in its history.

[26] A week later, Shapovalov became the third Canadian to win a junior Grand Slam singles title with a three-set victory over Alex de Minaur at the 2016 Wimbledon Championships.

[31] In March 2016, he reached the semi-finals of the Challenger Banque Nationale de Drummondville, beating his first top 100 player in Austin Krajicek before losing to Daniel Evans in three sets.

[37] In February 2017, Shapovalov was selected to play for the Canada Davis Cup team in the World Group 1st round tie against Great Britain, and lost his opener to Dan Evans.

In the deciding rubber against Kyle Edmund, he accidentally hit the chair umpire, Arnaud Gabas, in the eye after launching a ball aimlessly towards the crowd in anger after dropping serve in the opening stages of the third set, leading to immediate disqualification for unsportsmanlike behaviour, and as a result, Great Britain won the tie 3–2.

[55] Shapovalov began his 2018 season at the Brisbane International, where he lost in the first round in both singles, to Kyle Edmund, and doubles, to eventual winners Henri Kontinen and John Peers.

[62] Shapovalov started off his maiden clay court season at the Monte-Carlo Masters, where he lost in straight sets to qualifier Stefanos Tsitsipas in the first round.

Shapovalov handily defeated Jérémy Chardy and fiery Italian Fabio Fognini in straight sets,[79][80] before being knocked out of his home tournament in the Round of 16 by Robin Haase.

[82][83][84] In his second US Open appearance, 28th seed Shapovalov encountered long-time friend and fellow Canadian Félix Auger-Aliassime in a highly anticipated first-round match-up.

[89] At the Australian Open, he defeated Pablo Andújar and Taro Daniel before being stopped in four sets by six-time and eventual champion Novak Djokovic in their first singles match.

[95] At the Paris Masters, the tour's final tournament of the year, Shapovalov secured a top 20 year-end finish after beating Gilles Simon, Fabio Fognini, Alexander Zverev, and Gaël Monfils to reach the semi-finals.

[108] Three weeks later, in February, Shapovalov embarked on the European indoor hard court swing and entered the Open Sud de France as the third seed.

[110] But in the doubles tournament in Rotterdam, Shapovalov performed better, having reached the semi-finals with partner Bopanna after toppling fourth seeds Jean-Julien Rojer and Horia Tecău in the quarter-finals before losing to finalists Henri Kontinen and Jan-Lennard Struff.

[113] He and Bopanna also reached the quarter-finals of the doubles tournament after beating Jannik Sinner and Simone Bolelli, but the duo lost to Frederik Nielsen and Tim Pütz.

"[124] Additionally, Shapovalov and Bopanna reached their first Grand Slam doubles quarterfinal as a team after beating sixth seeds Krawietz and Mies in the second round.

[131] Shapovalov also played the doubles tournament with Bopanna and the pair made the quarter-finals after notching an upset win over top seeds Juan Sebastián Cabal and Robert Farah.

[140] Next, just three weeks after their prior encounter, Shapovalov faced a rematch against Simon at the Bett1Hulks Championship in his first match at the tournament, but the third seed lost this time after a poor serving performance that included thirteen double faults.

[155] In doubles, Shapovalov and Rohan Bopanna defeated top-seeded Juan Sebastián Cabal and Robert Farah in Madrid en route to the quarter-finals before they lost to Tim Pütz and Alexander Zverev.

[169][170] Heading to the US Open, Shapovalov defeated Federico Delbonis and Roberto Carballés Baena before losing to Lloyd Harris in straight sets in the third round.

[175] In the tour's closing European indoor hard court swing, Shapovalov attended the St. Petersburg Open, where he defeated Pablo Andújar before losing to Struff in the quarter-finals.

[184] Canada then won its maiden ATP Cup title over Spain after Shapovalov and Auger-Aliassime notched singles wins over Pablo Carreño Busta and Roberto Bautista Agut.

[197] In the next ATP 500 tournament the 2022 Erste Bank Open in Vienna he went one step further to reach his sixth final where he lost to top seed Daniil Medvedev.

[230][231] Australian tennis coach and former player Darren Cahill drew comparisons between Shapovalov's backhand and that of Stan Wawrinka, specifically noting how both their flexibility and racquet speed were the two main components that drove the power of the shot.

[233] However, due to the aggressive overall nature of his style of play, in addition to making many winners, Shapovalov is known to produce a similarly high amount of unforced errors in matches.

[256] At the 2019 Indian Wells Masters, Shapovalov debuted a sample of a rap he had quickly written before his third-round match after agreeing to the stadium emcee's request that he perform it for the crowd were he to win.

In 2020, during the suspension of professional tennis caused by the COVID-19 pandemic, Shapovalov began writing and experimenting with lyrics to record and he constructed his own in-home studio to produce his music.

The track honors the life he had lived as an athlete thus far, from developing during his childhood and overcoming those who had doubted him, to becoming a professional, which includes engaging with sponsors and contending with online critics, among other experiences.