Mercier was drafted from the United States National Development Team Program after previously playing with the St. Louis Heartland Eagles in the USHL.

As a senior Mercier was named the West regional MVP as he helped guide the Redhawks to the Frozen Four,[1] losing the 2008–09 National Championship game 4–3 in overtime to Boston University.

Expected to provide an energetic, physical presence, Mercier got off to a slow start recording a single assist in 24 games with Lake Erie before he was surprisingly recalled to the Avalanche on December 8, 2009.

Without a recall to the Avalanche, Mercier improved his goal totals with the Monsters each season and after his three-year tenure became Lake Erie's All-time games leader with 220.

[15] In the gold medal game, a 5–1 victory over Canada, Mercier gained notoriety when he was assessed a match penalty and ejected in the third period following a dangerous hit along the boards against Colton Yellow Horn.