Sony Corp.’s entertainment chief, Michael Lynton, is stepping down to devote his time to the chairmanship of the board of Snap Inc. ahead of its public stock offering planned for later this year.

Mr. Lynton, who along with his wife was one of the earliest investors in Snap, has been on the board of the technology firm best known for its messaging app Snapchat since 2013 and was quietly named its chairman late last year.

Long...