The actor has been the focus of press attention since it was revealed that Angelina Jolie has applied for divorce.
He narrated director Terrence Malick's epic documentary Voyage of Time, about the birth of the Universe.
He said he did not want his presence at the California Science Centre Imax Theatre in Los Angeles on Wednesday to "distract attention" from the film.
In a statement, Pitt said: "Terrence's Voyage of Time is an incredibly beautiful and unique experiential Imax film for children and families chronicling the birth of time.
"I'm very grateful to be part of such a fascinating and educational project, but I'm currently focused on my family situation and don't want to distract attention away from this extraordinary film, which I encourage everyone to see."
Cate Blanchett has narrated a different feature-length version of the film.  Pitt, 52, previously appeared in Malick's 2011 film Tree of Life.
Jolie, 41, has filed for divorce citing irreconcilable differences and asked for physical custody of their six children.
The couple married in 2014 after 10 years together. Jolie's lawyer Robert Offer said the actress had filed for the dissolution of the marriage "for the health of the family".
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Brad Pitt is to miss a premiere of his latest film to focus on his "family situation", he has said.