2008-09: Brendan O'Donnell scored 38 goals with 45 assists and 4 PIM in 38 games for the Winnipeg Wild in Manitoba midget hockey.
2009-10: O'Donnell played for the Winnipeg South Blues in the Manitoba Junior Hockey League. He scored 29 goals with 32 assists and had 55 PIM in 53 games. In four playoff games, he scored 2 goals with 1 assist as the Blues were swept by the Winnipeg Saints. O'Donnell was named MJHL Rookie of the Year and played for silver medal-winning Canada West at the World U-17 Challenge. He committed to play college hockey at the University of North Dakota in 2011-12. O'Donnell was selected by the Des Moines Buccaneers in the second round (18th overall) of the USHL Entry Draft but will play for the Penticton Vees in the BCHL next season.
2010-11: O'Donnell was the second-leading scorer for the Penticton Vees of the BCHL in his final season of junior hockey. The Flin Flon, Manitoba native scored 29 goals with 43 assists and had a league-high 18 power play goals in 58 games with the Vees, who finished second in the BCHL's Interior Division. O'Donnell had 1 goal with 5 assists and 9 PMs in six playoff BCHL playoff games.
2011-12: O'Donnell skated in 17 games for the University of North Dakota as a freshman — missing time early in the year due to a leg injury and then suffering a shoulder injury that required season-ending surgery in February. Playing primarily on the Fighting Sioux third line, he scored 5 goals with 1 assist and was plus-one. North Dakota finished fourth in the WCHA regular season but defeated regular season champion Minnesota and Denver on back-to-back nights to win the league's Broadmoor Championship Trophy and earn a bid to the NCAA Tournament.
O'Donnell is a big and solidly built two-way forward who uses his hockey sense and strength to create scoring chances. He is a well-rounded player who takes care of both ends of the rink.