Dantley was a forward at Notre Dame from 1973–76. He was a consensus first-team All-American in 1974–75 and 1975–76. He ranks second on the Notre Dame career scoring list with 2,223 points and holds the school record for free throws made (615) and free throws attempted (769).
Dantley had a stellar collegiate career for the Fighting Irish. As a freshman, he played an important role in one of the biggest games in college basketball history, Notre Dame's 1974 upset to end UCLA's record 88-game winning streak. That UCLA team, coached by John Wooden, featured Bill Walton, Jamaal Wilkes (then known as Keith Wilkes), and Dave Meyer.
Dantley led Notre Dame in scoring in 1974–75 (30.4 points per game) and 1975–76 (28.6 points per game), while also leading the team in rebounding those two seasons with marks of 10.2 and 10.1 rebounds per game, respectively. He was also the leading scorer on the 1976 US Olympic team that captured the gold medal in Montreal.
In the 1976 NBA draft Dantley was drafted sixth overall by the Buffalo Braves. He became the third Buffalo player in five years to receive the NBA Rookie of the Year Award when he won it after the 1977 season. Dantley bounced around the league after his rookie campaign. Buffalo traded Dantley to the Indiana Pacers before the 1977-78 NBA season season, making him the first NBA Rookie of the Year to be traded following his rookie season. Indiana traded him after 23 games to the Los Angeles Lakers. He stayed with the Lakers through the following season before being traded again, this time to the Utah Jazz. It was the third time in two years that he had been traded; the Jazz were his fourth team in as many years in the league.
In Utah, Dantley reached his peak establishing his reputation as a prolific scorer, twice leading the league in scoring (in 1981 and 1984). He averaged over 30 points per game each season between 1981 and 1984, though he missed 60 games in 1983 after tearing ligaments in his right wrist. In his seven years with the Jazz, Dantley picked up all six of his All-Star appearances and two All-NBA second-team honors.
Dantley finished his career with an average of 24.3 points per game. He scored his points with a mix of flat-footed mid-range jump shots, high-percentage opportunities close to the basket, and frequent trips to the free throw line. For his career, he shot .540 from the floor — 16th in NBA history — and .818 from the free throw line. He led the league in free throws six times and ranks sixth all-time in that category. He shares the record with Wilt Chamberlain for most free throws made in a regular-season NBA game with 28.
Utah retired Dantley's uniform number (#4) on April 11, 2007.
Dantley enjoyed outstanding success at every level of basketball, including high school, college, Olympics, NBA, and on April 7, 2008, he was elected to the Basketball Hall of Fame, 16 years after he retired.
Dantley later worked for the Denver Nuggets as an assistant coach for eight seasons. He briefly served as the team's head coach during the 2009-10 season, filling in for George Karl, who was fighting cancer.