Eliis selected at the NBA Draft in 1983 by the Dallas Mavericks. In his first three years in Dallas, he could not recommend it for the starting grid, so that he was transferred to the Seattle SuperSonics. In Seattle, Ellis developed immediately to the star of the team, increasing its yield point within a year by 7.1 points to 24.9 points per game. He was awarded the NBA Most Improved Player Award for this achievement. During his time with the Sonics to Ellis established himself as one of the most dangerous shooters in the league. 1988-89, he scored 27.9 points per game and was first appointed to the NBA All- Star Game. The All -Star Game he scored 27 points for the Western Conference.
In 1991, he transferred to the Milwaukee Bucks for Ricky Pierce. Although he came from the bench, Ellis scored consistently over 20 points per game. With his move to the San Antonio Spurs and Ellis got his place back in the starting lineup. He remained a consistent scorer and reached for the first time since 1989, again the playoffs. Ellis then played three years for the Denver Nuggets, before he returned to the Sonics in 1997. In spite of its already 37 years Ellis was still a feared shooter and scored 17 points per game and hit almost 50% of his three throws.
His last years were spent Ellis NBA again in Milwaukee and the Charlotte Hornets before he retired at the age of 39 years.
Ellis scored in his 17 -year career 15.7 points and 3.5 rebounds and hit 40.3 % of his three-point throws. In the all-time best list he is with this hit rate in eleventh place among the non-active players (as of 26 August 2011). In addition, Ellis holds the NBA record for most minutes played in a game: In the 154-155 defeat of his Sonics against the Bucks on 9 November 1989 Ellis was 69 minutes on the field and scored 53 points.