Bob McMahon began his professional lacrosse coaching career as an assistant coach with the Detroit Turbos in 1992 and 1993. In 1999, McMahon was hired as an assistant coach to his friend Terry Sanderson in Albany, and was promoted to head coach following the 2001 season, when Sanderson left Albany to become head coach of the expansion Montreal Express. In the two years with Sanderson as head coach, the Attack finished with 6-6 and 5-9 records, but in McMahon's first year as head coach, Albany improved to a league-best 14-2 record. The Attack hosted the NLL Championship game, which they lost to the Toronto Rock, but McMahon was named 2002 NLL Coach of the Year (an award later renamed the Les Bartley Award). McMahon was also selected as coach of the South team in the 2002 NLL All-Star Game.
After a disappointing 8-8 2003 season, the Albany Attack franchise moved to San Jose, and McMahon found himself out of work again. He was hired by his former assistant coach in Albany, Bob Hamley, as an assistant coach of the new Arizona Sting franchise. After four years as an assistant coach in Arizona, McMahon was announced as the new head coach of the Colorado Mammoth in September 2007, after Gary Gait announced that he was stepping down. He was relieved of his duties on January 19, 2010 following an 0-2 start to the 2010 season. Just two months later, Bob Hamley was hired as the new Mammoth head coach, and in an interesting twist, he requested that the Mammoth re-hide McMahon to be one of his assistant coaches, which they did.
- "Breaking: Bob Hamley takes over head coaching duties in Colorado, Bob McMahon back on Mammoth bench". NLLInsider. Mar 22, 2010. Archived from the original on March 24, 2010. Retrieved 2010-03-22.
- "Sanderson resigns in Albany, hops to Montreal". Outsider's Guide to the NLL. May 15, 2001. Archived from the original on 2007-08-18. Retrieved 2007-09-26.
- "McMahon named Coach of the Year". Outsider's Guide to the NLL. April 9, 2002. Archived from the original on November 14, 2003. Retrieved 2007-09-26.
- "Rock, Attack, K'Hawks pack All-Star rosters". Outsider's Guide to the NLL. April 2, 2002. Archived from the original on August 7, 2007. Retrieved 2007-09-26.
- "Bob McMahon named Colorado Head Coach". NLL.com. September 26, 2007. Retrieved 2007-09-26.
- "Heritage Cup this weekend". NLL.com. October 14, 2004. Retrieved 2007-09-26.
- "Who says nice guys finish last?". Outsider's Guide to the NLL. April 15, 2002. Archived from the original on August 29, 2008. Retrieved 2007-09-26.
| NLL Coach of the Year Award