In mid-July 2019, Morris signed as a free agent with the Knicks. The forward made his New York debut during the first game of the season, Oct. 23 against the Spurs, racking up 26 points, four rebounds, a season-high three steals and one assist. He'd reach his season-high three steals on three more occasions. A week later in a game against the Magic, Morris blocked a season-high four shots. On Nov. 20 in a game against the 76ers, Morris produced season highs in both rebounds (13) and assists (six) while also adding 22 points and two steals. That was one of Morris' three double-doubles. During a game against the Clippers on Jan. 5, the veteran scored a season-high 38 points, also adding five rebounds, two steals, one assist and one block. Just over a month later, he was traded to the Clippers in a three-team trade that also involved the Wizards. Morris made his Clippers debut Feb. 9 in a win over the Cavaliers, totaling 10 points, four rebounds, three steals and two assists. Through the rest of the regular season, including seeding play in the NBA bubble, Morris averaged 10.1 points, 4.1 rebounds and 1.4 assists. During the first round of the playoffs against the Mavericks, Morris averaged 12.8 points, 5.7 rebounds, 2.0 assists and 1.3 steals while shooting 53.7 percent from the field, 53.8 percent from three and 100 percent from the free-throw line. In the Clippers' second-round series against the Nuggets, he averaged 10.9 points, 4.1 rebounds and 1.3 assists while shooting 47.4 percent from the free-throw line, 42.4 percent from three and 88.9 percent from the free-throw line. Arguably Morris' best playoff performance was Game 1 against Denver, with Morris racking up 18 points (7-10 FG, 4-5 3Pt), five rebounds, two assists and two steals.

Across nearly every statistical category, Morris improved from his previous season with the Celtics, including points (13.9), rebounds (6.1), assists (1.5), field-goal percentage (44.7), minutes (27.9), three-point percentage (37.5), and free-throw percentage (84.4). Morris' free-throw percentage hit a career-high in 2018-19 while staying on par with attempts compared to past seasons. Morris had a strong stretch from Nov. 26 to Dec. 14 in which he averaged 18.8 points, 6.1 rebounds and 1.9 assists while shooting 52.9 percent from the floor, 46.0 percent from three, and 95.0 percent from the free-throw line. He had his best game of the season during a win against New Orleans, posting 31 points, four assists, and four rebounds while shooting 10-of-15 from the floor. His performances during this stretch were a huge reason why Boston went on an eight-game win streak. Morris and the Celtics entered the playoffs with a 49-33 record. They faced the Pacers in the first round, sweeping the fifth seed. In that time, Morris averaged 12.3 points and 6.5 rebounds. In the next round, the Celtics played the Bucks. Though the Celtics eventually lost the series, Morris was integral to the team's first win. Morris was able to play tough defense, blocking Milwaukee three times and grabbing seven rebounds.

In July, 2017, the Pistons traded Marcus Morris to Boston for Avery Bradley and a 2019 2nd round draft pick. The new acquisition immediately established himself as a big part of Boston's rotation. Having quickly earned the trust of head coach Brad Stevens, Morris averaged 26.8 minutes per game over the course of 54 appearances. He also made 21 starts. The rugged forward was forced to miss nine of Boston's first 11 games due to left knee soreness. That same knee issue forced him to miss another 11 games in December. But Morris still averaged double figures in scoring (13.6) for a fourth straight season. He had nine games with 20 or more points and a pair of contests in which he finished with 30 or more. His best performance of the year was a massive 31-point, nine rebound effort in a tight one-point loss to the Wizards on Mar. 14. The University of Kansas product chipped in a career-high 5.4 rebounds per game for good measure. Morris's per 36-minute numbers - 18.3 points, 7.2 rebounds, 1.8 assists, 0.9 steals - were excellent. Morris was also one of Boston's best players in the postseason. Playing in all 19 games, the former No. 14 overall selection (2011) posted double figures in scoring in all but four contests and logged a pair of double-doubles including a 14-point, 12-rebound performance in Boston's Game 7 loss to Cleveland in the Eastern Conference Finals.

Marcus Morris returned to Detroit in the 2016-17 season for another year of steady minutes as a key cog in the Pistons' starting rotation. Coach Stan Van Gundy once again had Morris start every game in which the big man appeared. The durable forward played in 79 games, the fifth season in a row in which Morris played in 77 or more contests. On Feb. 3, Morris scored a career-high 36 points in a win over the Timberwolves. On Feb. 28, Morris established a new career best with 37 points in a home win over Portland. For the season, Morris scored 15 or more points in 31 games. "Mook" delivered per-game averages of 14.0 points, 4.6 rebounds, 2.0 assists and a career-high 1.5 made three-pointers per contest. Morris drained three or more three-pointers in 17 games. He also shot a career-high 78.4 percent from the free-throw line.

The 2015-16 season was Marcus Morris' fifth season in The Association. In July, the versatile forward was traded by Phoenix with Reggie Bullock and Danny Granger to the Detroit Pistons for a 2020 second-round draft pick. The deal worked out well for Detroit, as Morris posted career-high per-game averages in points (14.1), rebounds (5.1) and assists (2.5). The 26-year-old also played in 80 games, the third season in a row the durable Morris appeared in 80 or more contests. Morris also shifted from primarily serving as a bench player with Phoenix to a regular starter with the Pistons, In fact, Morris started each of his 80 games with Detroit and his minutes per contest went up from 25.2 in 2014-15 to 35.7 with the Pistons. Morris' nearly 36 minutes per contest ranked 10th in the NBA. On Nov. 11, Morris swiped a career-high five steals in a loss at Sacramento. On Dec. 2, the rugged forward grabbed a career-high 14 rebounds along with 24 points in a home win over the Suns. On Feb. 24, Morris dished a career-high eight assists in a win over Philadelphia. Morris' Pistons finished 44-38, good enough for the eighth seed in the Eastern Conference. This marked the first time Morris had ever appeared in a playoff game. He started all four playoff matches for Detroit, averaging 17.8 points a game in the first-round series versus Cleveland. Despite Morris' efforts, the Pistons were swept by the LeBron James-led Cavaliers.

Marcus Morris started the 2014-15 season by signing a four-year contract extension with the Suns in September. His twin brother Markieff also signed a September extension with Phoenix. Marcus then went on to appear in 81 games (35 starts) and record per-game career highs in points (10.4), rebounds (4.8), assists (1.6), made three-pointers (1.4) and minutes (25.2). On Nov. 17, Morris dished out a career-high seven assists, plus 13 points, during a win at Boston. During a Dec. 26 win at Sacramento, Morris buried a career-high six three-pointers, shooting 6-for-7 from behind the arc and scoring 20 points. On Feb. 6, Morris posted a career-high 34 points, to go with 12 boards and five three-pointers, in a win over the Jazz. That performance was good for Morris' first ever NBA double-double. On March 19, Morris grabbed a career-high 13 rebounds during a win over the Pelicans. On March 22, Morris delivered another double-double of 11 points and 11 boards to go with seven assists in a win over the Mavericks. Morris registered five double-doubles during the season.

Marcus Morris played in all 82 regular-season games for the Phoenix Suns during the 2013-14 season and received one start. The 24-year-old produced career-high per-game averages for points (9.7), rebounds (3.9), assists (1.1), steals (0.9) and made three-pointers (1.2). He also played a career-best 22 minutes per game while shooting a career-high 44.2 percent from the field, to go along with 38.1 percent from three-point range and 76.1 percent from the charity stripe. On Nov. 5, Morris grabbed a season-high nine boards, to go with 16 points, in a win at New Orleans. On Dec. 10, "Mook" scored a season-high 22 points in a win over the Lakers. Morris drained a career-high five three-pointers (5-6 3Pt) during a Dec. 23 win over the Lakers. On April 16, Morris matched his season high of 22 points, and added six rebounds, during a road win over the Kings.

Marcus Morris split his sophomore season in The Association between the Houston Rockets and the Phoenix Suns. He also played a career-high 77 games. Morris returned to Houston to start the season and was a big contributor off the bench. He played in 54 of the Rockets' first 55 games, including 17 starts, and posted 8.6 points, 4.1 rebounds and 1.4 made threes during 21.4 minutes per contest. On Dec. 29, Morris generated a career-high 24 points in a loss to the Thunder. However, just prior to the trade deadline on Feb. 20, Morris was part of a three-team trade that reunited the power forward with his brother Markieff in Phoenix. Unfortunately, Marcus' role in Phoenix decreased relative to his time in Houston. In 23 games with the Suns, he scored 5.7 points in 16.1 minutes per game, logging six starts. Counting both stints, Morris averaged 7.7 points and 3.6 rebounds in 19.8 minutes per contest.

Marcus Morris was drafted in the first round (14th overall) of the 2011 NBA Draft by the Houston Rockets. He was taken just after his twin brother Markieff was selected by the Suns with the 13th pick. Marcus made his NBA debut on Opening Night, Dec. 26, during which he saw four minutes of playing time and committed two fouls. The late start to the campaign was as a result of the lockout. After brief appearances in Houston's first three games, the Rockets sent Morris to the D-League Rio Grande Valley Vipers. Morris played in 11 games for the Vipers and delivered per-game averages of 20.7 points, 8.3 rebounds, 1.3 steals and 1.1 made threes per contest. He returned to the Rockets in late February, but he struggled to see much playing time. On March 22, Morris scored a season-high eight points during a blowout win over the Warriors.