Ratner was accused of sexual misconduct in 2017 by several women, which he denied. Warner Bros. cut ties with him and his company in 2018.
WarnerMedia, which is owned by AT&T, said it is continuing to work with a third-party law firm to complete its investigation with Tsujihara's cooperation.
Tsuijhara, 54, had been with the WarnerMedia unit for more than 24 years. He became CEO in early 2013 and became chairman position later that year. Tsuijhara, the first executive of Asian decent to head a major Hollywood studio, led Warner Bros. to have its most profitable year ever in 2017.
However, also under Tsuijhara's tenure, Warner Bros. struggled to produce DC superhero films at the same caliber of its counterparts at Disney and Marvel Studios. It wasn't until 2017's "Wonder Woman" that the studio found true success, taking in $821 million in ticket sales worldwide. A year later, "Aquaman" became the first DC film to cross the $1 billion mark.
After first announcing a deal to acquire Time Warner in 2016, AT&T closed the merger in June 2018. With Tsuijhara's departure, all of the management that joined AT&T from Time Warner is now gone. Jeff Bewkes, former CEO of Time Warner; John Martin, former CEO of Turner and Richard Plepler, former CEO of HBO, have all departed the company in the last year.
AT&T's stock remained relatively unchanged in midday trading.