Director Otto Preminger offered the role of a Southern senator to Martin Luther King Jr., believing that the casting could have a positive impact (despite the fact that there were no black senators at the time). King declined after serious consideration, as he felt playing the role could cause hostility and hurt the civil rights movement.
"Advise & Consent" was the first mainstream film to feature a scene set inside a gay bar.
Peter Lawford was cast because Otto Preminger valued his access to the Kennedy family. Lawford was John F. Kennedy's brother in law, and JFK was also a massive movie buff who loved having a film crew around the White House.