Lee showed talent for basketball since an early age,and he impressed many college scouts with his game style. He accepted an offer to play for Marquette, starring there from 1974 to 1978. In 1974 Lee asked his coach Al McGuire to allow him to play for the United States Olympic basketball team. However, his coach had sent someone else and Lee went to Puerto Rico where he qualified for the Puerto Rican national basketball team. When Puerto Rico played against the U.S. in the 1976 Summer Olympics, Lee made 15 out of 18 field goals and scored 35 points. The U.S. still avoided an upset, defeating Puerto Rico by one point, 95-94.
In 1977, Lee led Marquette to the Final Four in what McGuire had announced would be his final season. The Warriors defeated UNC-Charlotte 51-49 in the semifinal round when Lee found Jerome Whitehead with a length of the court pass for a score just before the buzzer. In the final against North Carolina, Lee scored 19 points and led the Warriors to a come-from-behind 67-59 victory to secure the national championship. Lee was named the tournament's most outstanding player.
During Lee's first season in the NBA (1978-79), he started with the Hawks averaging 7.7 points per game during 49 games. He was traded to the Cleveland Cavaliers, where he enjoyed what were perhaps his best games in the league, scoring 11.5 points per game in the remaining 33 games of the season. He ended up scoring an average of 9.6 points per game in his first season in the NBA. Lee led the league in games played with 82.
After three games with the Cavs in the 1979-1980 season, Lee suffered an injury that would prove to be too big of an obstacle for him to overcome as far as his basketball career was concerned. He only scored 1.3 points per game on those three games. Before the season was over, he would be traded once again, to the Los Angeles Lakers, where, he played alongside Magic Johnson and Kareem Abdul-Jabbar, among others, for eleven games, before his injury recurred, forcing him to retire. He did, however, win an NBA championship ring, as the Lakers went on to beat the Philadelphia 76ers in that season's NBA Finals.
Lee's NBA stats in 96 games are 779 points with an 8.1 PPG average, 307 assists with a 3.2 APG average, 137 rebounds with a 1.4 RPG average, 87 steals with a 0.9 SPG average, a .450 field goal percentage, and a .761 free-throw percentage.