He served as the assistant coach to four National Basketball Association (NBA) team; the Boston Celtics (1972–77), the Milwaukee Bucks (1977–1983), the New Jersey Nets (1983–85), the Houston Rockets (1989–1993).
Killilea was hired by the Topeka Sizzlers of the Continental Basketball Association (CBA) as their head coach in 1986 and served in that capacity until he was fired in January 1988 after being called for 15 technical fouls and ejected from three games.
Upon his release from the hospital, Killilea was medically cleared to try out for the varsity Boston University basketball team.
[4] Killilea was head coach of the Melrose and Silver Lake high school basketball teams.
United Press International reporter Michael V. Uschan wrote an article on March 20, 1981, titled "Nelson matures as Bucks coach".
[10] After the season a New York Post report cited several anonymous Nets players who blamed their poor performance on an ongoing feud between Killilea and assistant coach Herman Kull.
Nets' owner Joe Taub and head coach Stan Albeck approached the Post reporter, Steve Baronfeld, telling him that Kull suffered a heart attack after reading the story.
"[10] Killilea was hired as the head coach for the Topeka Sizzlers of the Continental Basketball Association (CBA) in July 1986.