Mercredi started out in junior hockey with the Tier II Penticton Broncos of the British Columbia Hockey League, winning the Most Valuable Player in that league in 1970-71. He went up to major junior with the New Westminster Bruins in 1971-72 and 1972-73. The Atlanta Flames picked him 16th overall in the 1973 NHL Amateur Draft. He failed to make the team in 1973-74, playing in the minor pros. In 1974-75 he earned a two game callup. He junped to the World Hockey Association's Calgary Cowboys in 1975-76, but with little success.