Harrick's coaching career began at Morningside High School in Inglewood, California where he served as an assistant coach from 1964-1969 and as head coach from 1970-1973. He was then hired as an assistant coach at Utah State from 1974-1977. Harrick then spent two seasons as an assistant coach at UCLA from 1978-1979. His first collegiate head coaching job was at Pepperdine University in 1979, where he led the school to four NCAA Tournament appearances and was a conference coach of the year four times.
In 1988, he returned to UCLA to assume head coaching duties. During the recruiting period before his first season, he recruited Don MacLean which was the most significant recruit to commit to UCLA in several years and helped start a revival of the basketball program. During the 1994-1995 season, he led UCLA to a then-school record 31-2 record and the school's eleventh national championship, its first since the 1974-75 season. He left UCLA as the school's second-winningest coach.
After a one-year hiatus, Harrick returned to coaching by accepting the head coach position at Rhode Island. He coached the Rams for two seasons (from 1997-99), where in both years they qualified for the NCAA Tournament. During the 1998 tournament, the Rams upset Kansas in the second round and reached the Midwest Regional finals. In his second season, he managed to recruit Lamar Odom and led the Rams to their first Atlantic 10 Conference title.
After the season, he left URI to become the head coach at the University of Georgia. He served there for four seasons (1999-00 through 2002-03), leading the Bulldogs to the NCAA tournament twice following a losing record.
After Georgia, Harrick worked as a scout for the NBA's Denver Nuggets and helped develop basketball in China.