Activision Blizzard Inc. on Wednesday unveiled a roster of sports-team owners and videogame-industry veterans involved in an esports league it pledged to launch before the end of the year.

The company is building a league around “Overwatch,” betting on a year-old shooter videogame with a cartoonish bent that has more than 30 million registered players but lacks the lineage of a franchise such as “Call of Duty.”

Activision...