The Wall Street Journal is a launch partner for Apple Inc.’s $9.99-a-month news service, marking a significant shift in strategy meant to draw in new readers and paying subscribers without undercutting the publication’s core business.

Apple unveiled the news app, Apple News+, at an event Monday. It will provide access to articles from more than 300 magazines including Vogue, GQ and Sports Illustrated. In addition to the Journal, the Los Angeles Times and Toronto Star will be the other North American newspapers joining the...