Sipple was born in Detroit, Michigan. He served in the United States Marine Corps and saw action in Vietnam. Shrapnel wounds suffered in December 1968 caused him to finish out his tour of duty in a Philadelphia veterans hospital, from which he was released in March 1970. He later spent six months in San Francisco's VA hospital, and was frequently readmitted into the hospital in 1975, the year he saved Ford's life.
Listed as being totally disabled on psychological grounds, he was unable to hold a job and was receiving disability pay. He lived with a merchant seaman roommate, in a fourth-floor walk-up apartment located in San Francisco's Mission District. Sipple was active in local causes, including the historic political campaigns of openly gay City Council candidate Harvey Milk.
Sipple was part of a crowd of about 3,000 people who had gathered outside San Francisco's St. Francis Hotel to see President Ford on September 22, 1975.
Ford, just emerging from the building, was vulnerable despite heavy security protection. Sipple noticed a woman next to him had pulled and leveled a .38-caliber pistol at Ford as he headed to his limousine. Reacting instinctively, Sipple lunged at the woman, Sara Jane Moore, just as her finger squeezed the trigger. While the gun did go off, the impact was enough to deflect her aim and cause the bullet to veer wide of its mark. The bullet hit John Ludwig, a 42-year-old taxi driver. Ludwig survived.
The police and the Secret Service immediately commended Sipple for his action at the scene. President Ford thanked him with a letter The White House waited three days before publicly thanking Sipple, while staff debated an appropriate response after learning that the heroic Sipple was gay. and the news media portrayed Sipple as a hero.
Though he was known to be gay among members of the gay community, and had even participated in Gay Pride events, Sipple's sexual orientation was a secret from his family. He asked the press to keep his sexuality off the record, making it clear that neither his mother nor his employer had knowledge of his orientation; however, his request was not complied with. The national spotlight was on him immediately, and Milk responded. While discussing whether the truth about Sipple's sexuality should be disclosed, Milk told a friend: "It's too good an opportunity. For once we can show that gays do heroic things, not just all that ca-ca about molesting children and hanging out in bathrooms." Milk contacted the newspaper.
Several days later Herb Caen, a columnist at The San Francisco Chronicle, exposed Sipple as a gay man and a friend of Milk. Sipple was besieged by reporters, as was his family. His mother, a staunch Baptist in Detroit, refused to speak to him. Sipple sued the Chronicle for invasion of privacy. Of President Ford's letter of thanks to Sipple, Milk suggested that Sipple's sexual orientation was the reason he received only a note, rather than an invitation to the White House.
Sipple filed a $15 million invasion of privacy suit against Caen, seven named newspapers, and a number of unnamed publishers, for publishing the disclosures. The Superior Court in San Francisco dismissed the suit, and Sipple continued his legal battle until May 1984, when a state court of appeals held that Sipple had indeed become news, and that his sexual orientation was part of the story.