After being selected by the Atlanta Hawks in the second round of the 2013 NBA draft, Ennis moved to Australia and helped the Perth Wildcats win the 2014 NBL championship.

He debuted in the National Basketball Association (NBA) in 2014 with the Miami Heat and later played for the Memphis Grizzlies, New Orleans Pelicans, Detroit Pistons, Houston Rockets, Philadelphia 76ers, Orlando Magic, Brooklyn Nets, Los Angeles Clippers and Denver Nuggets over eight NBA seasons.

Born in Ventura, California, Ennis grew up in the Westview Village housing project where he and his five siblings played basketball, soccer, rode bikes and skateboarded.

[2] For his junior season, Ennis joined the Long Beach State 49ers,[3] and immediately garnered the starting small forward role.

At the end of the season, Ennis was named Big West Player of the Year[5][6] and an AP honorable mention All-American.

[7] On April 5, 2013, Ennis scored a team-high 13 points in the Reese's College All-Star Game, leading the East team to an 87–81 win over the West.

[14] He went on to earn Player of the Month honors for October after averaging a league-leading 24.0 points per game to begin his career.

[19] In Game 2, Ennis endured a quieter-than-usual night, tallying just 14 points before fouling out with 22 seconds left in an 89–84 loss.

[20] In Game 3, Ennis' early foul trouble limited him to a season-low nine points as the Wildcats claimed a 93–59 victory to win the championship.

[24] Following the conclusion of the 2013–14 NBL season, Ennis moved to Puerto Rico to play for Piratas de Quebradillas of the Baloncesto Superior Nacional.

With the Heat up by four points with less than nine minutes to go in the fourth quarter, Ennis brought the American Airlines Arena crowd to their feet with a spectacular three-point play, taking off from midway down the paint, elevating over Rasual Butler and throwing down a dunk while getting fouled.

[36] With $845,059 guaranteed salary on the line for Ennis coming into the 2015–16 season, he struggled during the 2015 NBA Summer League, calling his play "terrible" after shooting 29.7 percent from the field (19-of-64) in seven games, including 2-of-23 on three-pointers, and recorded more than twice as many turnovers (23) as assists (11).

[37] Despite sustaining a dislocated finger on his left hand in Miami's exhibition finale against the New Orleans Pelicans, the Heat retained Ennis for the 2015–16 season after earning a spot on the team's opening night roster.

[38][39] Ennis managed game time in three of the Heat's first seven games to begin the 2015–16 season, when on November 10, 2015, he and Mario Chalmers were traded to the Memphis Grizzlies in exchange for Jarnell Stokes and Beno Udrih,[40] a deal undertaken in order for the Heat to cut $6 million in luxury tax.

He subsequently spent the majority of the 2015–16 season in the NBA Development League playing for the Iowa Energy, the Grizzlies' affiliate team.

However, a loss to the Sioux Falls Skyforce on March 29 ended their streak, as they were eliminated from the playoff race with two games remaining in the season.

[53] On March 30, 2016, Ennis signed a 10-day contract with the New Orleans Pelicans to help the team deal with numerous injuries.

[54][55] He made his debut for the Pelicans later that night, recording 13 points, 5 rebounds and 4 assists in 24 minutes off the bench in a 100–92 loss to the San Antonio Spurs.

[58] Later that day, in his seventh game and third start for the Pelicans, Ennis recorded 18 points, 6 rebounds and 3 steals in a 121–100 loss to the Phoenix Suns.

[61] On July 13, 2016, Ennis signed a two-year, $6 million contract with the Memphis Grizzlies, returning to the franchise for a second stint.

[62][63] In the Grizzlies' season opener on October 26, 2016, Ennis recorded 15 points and six rebounds in 28 minutes as a starter in a 102–98 win over the Minnesota Timberwolves.

[69] On February 8, 2018, the Grizzlies traded Ennis to the Detroit Pistons in exchange for Brice Johnson and a 2022 second-round draft pick.

[83] On July 12, 2019, Ennis re-signed with the 76ers,[85] agreeing to a two-year, $4.1 million deal with a player option for the second year.

[88][89] His addition and insertion into the starting lineup coincided with the Magic's offensive outburst and 8–4 stretch before the league paused on March 11 due to the COVID-19 pandemic.

He helped the team reach the final of the Khalifa Bin Salman Cup after recording a game-high 30 points, 10 rebounds, eight assists and two steals in a semi-final win over Muharraq.