Was the final member of the Hawaii Five-O (1968) TV series original cast to pass away.
MacArthur was the adopted son of actress Helen Hayes and playwright Charles MacArthur. His elder sister, the couple's biological daughter, Mary (for whom he named his own elder daughter), died in 1949 of polio. Hayes established the Mary MacArthur Fund, which helps children with polio along with the March of Dimes. Actress Lillian Gish was his godmother.
MacArthur was in talks to make a cameo appearance on the new Hawaii Five-0 (2010) series, but passed away before the details could be worked out.
Attended the same high school, Solebury School (New Hope, Pennsylvania) as first wife Joyce Bulifant. They both graduated in the same class (1955).
MacArthur had four children: Charles Pennock MacArthur, Mary Hayes (MacArthur) McClure, Juliette Nicole (MacArthur) Rappaport, James Duntz MacArthur, and seven grandchildren.
MacArthur formed a film production company called SouthWind Productions and planned to film his first project called "You Never Gave Me Roses" in the New Orleans area in March 1980. He was to be one of the stars. No evidence the film was ever made.