DeMarco was born in the United States while his father was playing for the American Hockey League (AHL) Cleveland Barons, but was raised in North Bay, Ontario.

DeMarco played his first two professional seasons in the CHL minor league, earning brief NHL call-ups to New York.

His 9 power-play goals for a blueliner that season ranked behind only Bobby Orr and Guy Lapointe.

DeMarco then jumped to the rival World Hockey Association, signing with the Edmonton Oilers for the 1977–78 WHA season.

DeMarco returned to the NHL for the 1978–79 season, signing with the Boston Bruins, but appeared in only three games for the team.