Comeau, 25, had zero points in 16 games with the Islanders this season. He scored 24 goals last season. He will make $2.5 million this season and be a restricted free agent July 1.
"Blake is a smart, committed, two-way hockey player who kills penalties, is responsible defensively and can score some goals as well," Flames general manager Jay Feaster said Friday. "We have liked this player for a long time, and our scouts and staff are convinced a change is going to be good for him. We are excited to add him to our club without having to give up an asset."
Comeau had career highs last season in goals, assists (22), points (46) and games played (77).