On January 21, 1933, she eloped to Tijuana, Mexico with a naval ensign, later to become four-star Admiral John S. McCain, Jr. in Caesar's Bar. She was attending the University of Southern California and McCain was attached to USS Oklahoma (BB-37). She became the daughter-in-law of Admiral John S. McCain, Sr., a noted World War II carrier admiral, under Fleet Admiral William Halsey. In 1952, she was the ship sponsor for USS John S. McCain (DL-3), named for her father-in-law. She was also an honored guest at the 1992 launching of USS John S. McCain (DDG-56) which was named for her husband and her father-in-law. She was also active in Navy Wives Clubs. For example, during Christmas 1971, she traveled to Saigon and presented $1,000 ($5,823 today) and 14 boxes of clothing to the Vietnam Advisory Board of Operation Helping Hand on behalf of the Pearl Harbor area Navy Wives Clubs.
Roberta McCain has three children. Jean Alexandra "Sandy" (McCain) Morgan (born 1934), John Sidney McCain III (born 1936), and Joseph Pinckney "Joe" McCain II (born 1942). As a Navy family, the couple moved around as the Navy required. Shortly after they were married, the McCains moved to Honolulu, Hawaii where her husband was stationed in 1933 to 1934 where their daughter was born. They returned to Pearl Harbor in 1968 from the Admiral's post in London as commander of US European Naval Forces where they lived at the time of their son's capture in Vietnam. It was in Pearl Harbor that the couple awaited the release of their son from captivity. In June 1968, Roberta McCain told Parade magazine, "Religion has been of great importance to us in our concern for Johnny, religion and the military tradition of my husband's family. We all pray for the time when we'll see Johnny again." In 1971, she requested no special sympathy for her in regards to her son's captivity. She said navy tradition was important in the family, her daughter married a naval officer, John McCain III became a naval aviator and her youngest son Joe enlisted in the Navy during the Vietnam war. Her son John was held as a prisoner of war in North Vietnam for five and a half years. When notified upon his release on March 15, 1973, that he had shouted expletives at his captors, Mrs. McCain's response was, "Johnny, I'm going to come over there and wash your mouth out with soap."
John McCain has said of his mother: "My mother was raised to be a strong, determined woman who thoroughly enjoyed life, and always tried to make the most of her opportunities. She was encouraged to accept, graciously and with good humor, the responsibilities and sacrifices her choices have required of her. I am grateful to her for the strengths she taught me by example."