Philippe Dauman, CEO of Viacom, has been named as Redstone's replacement.
By taking the chairman role, Dauman emerges victorious from a power struggle that he had been waging with Shari Redstone, daughter of Sumner Redstone.
Dauman is also in charge of Redstone's healthcare decisions, which Redstone's former companion, Manuela Herzer, has objected to.
Shari Redstone has been adamant that the people handling Redstone's personal matters, like the health directive, should not also be involved in his business interests like Viacom and CBS.
On Wednesday, news broke that Redstone had stepped down as chairman of CBS. The board of directors of CBS named CEO Les Moonves as Redstone's replacement.
The future of Viacom and CBS had been in limbo due to a power struggle that had taken on the feel of a soap opera. At the center remained Redstone, whose mental competence is now being questioned by his former girlfriend, Manuela Herzer, in a lawsuit.
The timing of the moves at Viacom and CBS appeared to confirm fears that an upcoming examination from a psychiatrist as part of the legal dispute with Herzer could confirm that Redstone is unable to fulfill the roles of chairman at those companies.
Herzer has claimed that Redstone is "a living ghost" who cannot stand, walk or make decisions. The healthcare directive that put Dauman in charge of his medical decisions has widely been called "an illegible scrawl."
Viacom remains one of the biggest players in cable television, running MTV, Comedy Central, Nickelodeon, BET, CMT and VH1. Movie studio Paramount Pictures is also owned by Viacom.
The cable TV business, however, is not what it used to be. Declines in subscriber totals and the prospect that cord cutting could accelerate in the coming years have eroded any confidence that cable TV production has better days ahead.
In the past year, Viacom's stock has lost more than one-third of its value.
