LOS ANGELES — For a dynastic drama that played out over decades, with sons falling in and out of favor and an aging father unwilling to loosen his grasp, the accession on Wednesday was anticlimactic: Lachlan Murdoch, as expected, was named chief executive and chairman of his family’s shrinking television conglomerate.

The job cements Mr. Murdoch, 46, as successor to his father, Rupert Murdoch, 87, who will take the title of co-chairman.

The news release from 21st Century Fox announcing Mr. Murdoch’s new duties at the “proposed new ‘Fox’” made no mention of his younger brother, James Murdoch, 45, who currently serves as chief executive of 21st Century Fox. James Murdoch is expected to strike out on his own, perhaps starting a company that invests in digital media businesses.

The management changes, which Rupert Murdoch telegraphed in December, were announced by 21st Century Fox as part of the proposed sale of the bulk of its assets to the Walt Disney Company. That $52.4 billion deal is awaiting shareholder and regulatory approval, although Comcast has been maneuvering to upend the agreement with a hostile bid. Either way, 21st Century Fox’s movie studio, its share in Hulu and cable networks, and stakes in overseas television providers will be sold.