Smith made 34 appearances out of 66 possible games for the Knicks during the conronavirus-shortened 2019-20 season. The young guard averaged 5.5 points, 2.9 assists, 2.3 rebounds and 0.5 made three-pointers in 15.8 minutes per game. He shot 34.1 percent from the field, 29.6 percent from three and 50.9 percent from the free-throw line. Smith missed 13 games in late December and January due to a strained oblique. On Feb. 24, Smith set a new career-high with seven steals against the Rockets. He also finished the game with 15 points (5-12 FG, 1-2 3Pt, 4-5 FT), seven rebounds and five assists in 29 minutes. The seven rebounds were also a season high and this game marked one of Smith's three starts. Smith's other single-game season highs were set at 17 points, eight assists, two threes and two blocks. Smith scored in double-digit six times, grabbed at least five rebounds six times and dished out at least five assists 10 times. He also got at least one steal in 14 games. In the nine games that Smith saw at least 20 minutes, he averaged 10.1 points, 5.2 assists, 3.2 rebounds and 1.6 steals.

The 2018-19 season marked Smith's second in the Association. The guard split his season between the Mavericks and the Knicks. First, he appeared in 32 games with Dallas (all starts), averaging 12.9 points, 4.3 assists, 3.0 rebounds and 1.3 steals across 28 minutes. On Oct. 28, Smith got hot and scored 27 points in a loss to Utah. A wrist injury forced Smith to miss a game on Nov. 26. The injury would linger, eventually forcing Smith to miss 10 of 11 games starting on Dec. 5. Then in mid-January, back issues would force Smith to miss six games. On Jan. 30, Smith had a triple-double and set career high in assists (15) during a 24-point win over the Knicks. One day later, Smith was involved in a six-player trade that brought Kristaps Porzingis to Dallas and Smith to those same New York Knicks. Smith proceeded to appear in 21 games (18 starts) with New York. With the Knicks, he averaged 14.7 points, 5.4 assists, 2.8 rebounds and 1.3 steals in 28.6 minutes per game. As a whole, he shot 42.8 percent from the field, 32.2 percent from three and 63.5 percent from the free-throw line. On Feb. 8, in a loss to the Pistons, Smith scored a career-high 31 points. In the 21 games that Smith saw at least 30 minutes, he averaged 17.2 points, 5.0 assists and 2.9 rebounds while recording a total of 27 steals and nine blocks.

Dennis Smith was selected ninth overall by the Dallas Mavericks in the 2017 NBA Draft. The rookie immediately saw extended playing time, averaging 29.7 minutes per contest over 69 games (all starts) with Dallas. Smith made his NBA debut on Opening Night, Oct. 18, delivering a double-double of 16 points and 10 dimes in a close loss to Atlanta. On Nov. 14, Smith generated a career-high 27 points while also recording six rebounds and two dimes in a loss to the Spurs. Smith would start 23 of Dallas' first 25 games before a hip injury cost him six games in mid-December. On Jan. 16, the rookie posted 25 points and five assists during a loss at Denver. On Feb. 11, Smith dished a career-high 11 assists to go along with 16 points during a loss at Houston. Smith would deliver 10 or more assists six times on the campaign and would reach the 11-dime mark twice after doing it in February. He had six double-doubles and scored in double figures on 57 occasions. Overall, Smith posted per-game averages of 15.2 points, 5.2 assists, 3.8 rebounds, 1.5 made threes and 1.0 steals per contest. He was also named to the 2017-18 All-Rookie Second Team.