Brennan began his coaching career at Chelsea Piers in 2013 and is the head coach for various 10 and Under and High School swim team groups.
A 2013 graduate of Loyola University Maryland, Brennan majored in International Business and was the captain of the Loyola University Men's Swim Team his senior year. A 3-time swimmer of the year in the Metro Athletic Conference, Loyola won the Men's Team Championship three out of his four years there.
Brennan was a former National Age group record holder in the 1650 Yard Freestyle for 13-14 year olds. He went on to compete at the 2008 and 2012 Olympic Trials and was a multi-time National finalist in the 400 IM and 1500 Freestyle. He has been ranked in the top 50 in the world in both the 400 IM and 1500 Freestyle. Brennan was a member of the 2009 World Championship team, where he competed in the 1500 Freestyle in Rome, Italy.