O'Connor died Wednesday in Phoenix of complications arising from Alzheimer's disease, the court said in a statement. He had been diagnosed with the disease nearly two decades ago.
After Sandra Day O'Connor became the first woman to serve on the nation's highest court in 1981, her husband gave up a partnership at a venerable Phoenix law firm to accompany her to Washington.
Soon after the couple arrived, a reporter asked him, "How do you feel about being in the supporting role?" He responded, "Sandra's accomplishments don't make me a lesser man. They make me a fuller man."
In Washington, he practiced at the law firm of Miller & Chevalier but in 1988 switched to another firm, Bryan Cave, which allowed him to spend time in Phoenix and take advantage of his contacts there.
A civic leader, the confident and witty O'Connor was once described as "a magnificent man full of Irish humor and tales," by family friend Alan K. Simpson, a former senator from Wyoming.
Fixtures on the Washington social circuit in the 1980s and 1990s, the couple were known for their ballroom dancing.
By 2000, O'Connor had retired, and as his condition worsened, he spent much of the workday with his wife. She retired from the court in 2006 to care for him, but within months had to place him in an assisted-living facility in Phoenix.
As his memory faded, he no longer recognized his wife of more than 50 years and struck up a romance with a fellow Alzheimer's patient. The O'Connor family publicly shared the poignant turn of events.
"Sandra sees this as a bright spot in his life that would otherwise be dark and lonely," former FBI Director William Webster, a family friend, told People magazine in 2007. "She felt if this gave him a little sunshine, why, that's great."
John Jay O'Connor III was born Jan. 10, 1930, in San Francisco, the son of physician John O'Connor II and his wife, Sally.
After earning a bachelor's from Stanford University in 1951, O'Connor met his future wife at Stanford's law school. They fell for each other while proofreading a law review article and then dated for the next 40 nights, she wrote in her memoir.
The couple married in 1952 at an Arizona cattle ranch that was her childhood home.
After he graduated from law school in 1953 and joined the Army, his wife accompanied him to Frankfurt, Germany, where he worked in the Judge Advocate General's Corps until 1956.
On returning to Phoenix, the O'Connors took the Arizona bar exam together.
In 1957, he joined the firm of Fennemore, Craig, von Ammon & Udall, and primarily handled general corporate matters before resigning in 1981.
In addition to his wife, O'Connor is survived by their three sons, Scott, Brian and Jay, and six grandchildren.
Services will be private.