MacCarthy was born in 1881 and grew up in Toronto where his father, Hamilton Plantagenet MacCarthy, was a sculptor. Coeur de Lion executed many busts of political figures including the bust of Queen Victoria for the alcove above the Speaker's Chair in the Senate Chamber. He worked with Dominion carver Cléophas Soucy on the figures for the Parliament Buildings including the lions at the entrance. MacCarthy set up a studio in Montreal in 1918. He is well-known for his sympathetic memorials for the CPR and the Verdun War Memorial. He died in 1979.