Immediately after graduating, Parker was named head coach at
Medford High School. After only one year, he returned to BU as an assistant under his former college coach,
Jack Kelley, and helped lead the Terriers to two consecutive national championships in 1971 and 1972. After Kelley left the program to become general manager and head coach of the
New England Whalers, Parker was promoted to B-team coach under his predecessor,
Leon Abbott. Abbott was abruptly fired on December 21, 1973 for withholding information about the eligibility of two Canadian players who had played
junior hockey in their native country, even though a judge questioned the constitutionality of the rules allegedly violated. Parker was named his successor. Parker was asked by USA Hockey about coaching the Olympic team for the 1980 Olympics. He declined the position, which opened the door for
Herb Brooks to serve as coach. On February 8, 1989, Parker was named Boston University's athletic director. He was going to step down as head coach at the end of the 1988–89 season, but on February 21, 1989, Parker announced he was relinquishing the AD's job to continue coaching. Parker was named the NCAA Coach of the Year three times, the first after the 1974–75 season, again after the 1977–78 season and a third time after 2008-09. Parker was also named the
Hockey East Coach of the Year after the 1985–86, 1991–92, 1999–2000, 2004–05 and 2005-06 seasons. On January 30, 2009, Parker claimed his 800th win in a 3-1 victory over
Merrimack College. He was only the third coach to win 800 games, and the first to do so with one team. On April 11, 2009, Parker won his 30th NCAA tournament game and third team national title. Parker retired at the end of the 2012-13 season. He finished with a record of 897–472–115. At the time of his retirement, he was the third-winningest coach in NCAA history, behind only
Ron Mason and
Jerry York. His 897 wins are far and away the most in BU history, and are more than four times the total of runner-up
Harry Cleverly. He has had a hand in more than two-thirds of BU's all-time wins. Apart from his one year as Medford High's coach, he spent the first 48 years of his adult life at BU as a player, assistant coach and head coach. ==Retirement==