Before playing in the NHL, Lamothe played 3 seasons in the OHL with the Kingston Frontenacs. He was drafted with the 92nd overall pick by the Montreal Canadiens in the 1992 NHL Entry Draft. He has played for the Fredericton Canadiens, Syracuse Crunch, Hamilton Bulldogs and Grand Rapids Griffins of the AHL, as well as the Wheeling Thunderbirds of the ECHL and the Indianapolis Ice of the IHL. When he left North America, he joined Lokomotiv Yaroslavl of the RSL. He also played for Severstal Cherepovets and SKA St. Petersburg. He played 15 games in the KHL with Barys Astana, 14 games in the SM-liiga with the Pelicans, and 15 games in the DEL with the Hamburg Freezers. His season with the Pelicans was cut short after he suffered a medial ligament tear in his knee. He returned to North America on November 23, 2010 after being released from the Freezers. He retired from playing professional ice hockey in 2011.