Westhead's tenure with the Lakers started and ended the same way: abruptly. He began the 1979-80 season as an assistant, but when head coach Jack McKinney suffered a near-fatal bike crash 14 games into the campaign, Westhead stepped in and guided the team all the way to its seventh NBA title. With Spencer Haywood suspended and a hobbled Kareem Abdul-Jabbar back in Los Angeles, Westhead gambled by starting 20-year-old rookie point guard Magic Johnson at center for Game 6 of the finals against the Philadelphia 76'ers. Johnson had one of the greatest games in finals history, finishing with 42 points, 15 rebounds, seven assists, three steals and a blocked shot as the Lakers closed out the series.
However, it didn't take long for the euphoria of that first season to wear dissipate. Despite winning 54 games the following year, the Lakers lost to Houston in the first round of the playoffs and it was clear the coach's methodical half-court style did not sit well with many of his players, who preferred an up-tempo, fast-break style. A common misconception is that it was Magic Johnson's public demand to be traded led to Westhead's departure, but in reality Lakers owner Jerry Buss wanted to fire Westhead several days prior to Johnson's comments. Thus, 11 games into his third season, with the Lakers off to a disappointing 7-4 start, Westhead was fired, despite having the second highest winning percentage of any coach in team history to that point, behind only the man he replaced, Jack McKinney. His replacement was one of his own assistants, a former Lakers player and broadcaster by the name of Pat Riley.
"It was just becoming a job," Johnson later said of his time under Westhead. "No high fives. No camaraderie. That was hurting me because that's what I'm all about--having fun playing basketball. But the way the system was then, nobody was having fun. We were just four guys looking to pass in to one."
It didn't take Westhead long to land another head coaching job. In 1982-83 he was hired by Chicago, but lasted only one season as the Bulls went 28–54. The Bulls had just traded star center Artis Gilmore to the San Antonio Spurs, and the franchise was still two years away from the debut of Michael Jordan.
Westhead, who had begun his coaching career at La Salle University, where he led the men's team to one NIT and two NCAA tournament appearances in nine seasons. After his brief stint in Chicago, he returned to the college ranks and turned tiny Loyola Marymount into a legitimate contender with the help of USC transfers Hank Gathers and Bo Kimble. Using the run-and-gun style Westfall had resisted with the Lakers, LMU earned three straight NCAA tournament berths from 1988-90.
In 1990-91, Westhead returned to the NBA with the Denver Nuggets, a position he held for two seasons. He coached George Mason University from 1993-97, tried his hand in the ABA in 2000-01 and in the Japanese Pro League (2001-03), then went back to the NBA as an assistant with the Orlando Magic from 2003 to 2005. In 2007, Westhead led the Phoenix Mercury to the WNBA championship, making him the only coach to win championships in the NBA and WNBA.