Their participation was announced Friday by telecast producers Brian Grazer and Don Mischer.
This will be the first time the composers have worked on the Oscar show.
"Hans is one of the most accomplished and creative film composers of our time and Pharrell is a phenomenal songwriter with an amazing list of credits," Grazer and Mischer said in a statement. "This is an exciting and prestigious collaboration that promises to take the audience on a musical journey."
"It is a great privilege to serve the academy in this role and to help celebrate and honor this year's incredible artistry," added Zimmer.
"I am honored to work with my mentor and teacher, Hans Zimmer, and I have wanted to collaborate with Brian Grazer on something for years," said Williams. "I cannot believe I will be joining them and their teams on the most prestigious show of the year, the Academy Awards."
The 84th Academy Awards will be presented Feb. 26.