Moore's career hit its peak in the 1960s. During that time, she guest starred in several popular shows of the era including Alfred Hitchcock Presents, Perry Mason, Bewitched, and The Real McCoys. One of her more notable recurring roles was as Sheriff Andy Taylor's love interest, Peggy "Peg" McMillan in four episodes of The Andy Griffith Show from 1962 to 1963. Moore was a guest star in television westerns like Wagon Train, Gunsmoke, The Rebel, and The Virginian. By the 1970s, her career began to wane because of drug and alcohol issues. She made her final onscreen appearance in 1986.
From 1963 to 1967, she was married to actor Ryan O'Neal, with whom she had two children: Griffin and Tatum O'Neal. Moore died of lung cancer in 1997.
Moore was born Dorothy Joanne Cook in Americus, Georgia, the elder of two daughters of Dorothy Martha (née English) and Henry Anderson Cook III. In 1941, when she was a child, her parents and younger sister were involved in a fatal car accident. Her mother and sister died immediately, while her father died a year after of the injuries he sustained in the accident. Moore was then adopted by a wealthy local family and changed her name from Dorothy to Joanna.
As a teen, she married and quickly divorced Willis Moore in 1951. After the divorce, she attended Agnes Scott College in Decatur, Georgia. While attending college, she entered and won a beauty contest and was brought to Hollywood. Moore's acting career began when a producer for Universal Studios spotted her at a cocktail party.
Moore made her television debut in the November 8, 1956, episode of Lux Video Theatre. The following year, she made her film debut in the 1957 crime drama Appointment with a Shadow. Later that year, she appeared in episodes of Goodyear Theater and Harbormaster along with another film, Slim Carter. In 1958, she had a small role in the film noir classic Touch of Evil with Orson Welles, Charlton Heston, Janet Leigh, and Marlene Dietrich, followed by more substantial roles in the horror film Monster on the Campus and the western Ride a Crooked Trail.
From 1958 to 1959, Moore landed guest spots on television, including Studio One, Suspicion, The Rough Riders, Bourbon Street Beat, Bat Masterson, The Real McCoys, and Riverboat. She made a guest appearance on Perry Mason as the title character in the 1958 episode "The Case of the Terrified Typist."
During the 1960s, Moore continued her career guest-starring on numerous television shows in addition to film appearances. From 1960 to 1961, she guest-starred on Five Fingers, The Rebel, Hong Kong, The Untouchables, 77 Sunset Strip, Going My Way, and Empire.
In 1962, Moore appeared as Miss Precious in Walk on the Wild Side with Jane Fonda, Barbara Stanwyck and Capucine, followed by the musical, Follow That Dream with Elvis Presley. That same year, Moore appeared in four episodes of The Andy Griffith Show as Peggy "Peg" McMillan, Sheriff Taylor's love interest. In 1963, she co-starred in Son of Flubber and was cast in The Man from Galveston, intended as the pilot for Temple Houston. Also that year she made a second guest appearance on Perry Mason as Grace Olney in "The Case of the Reluctant Model." In 1964, she guest-starred on Bob Hope Presents the Chrysler Theatre.
From 1965 to 1967, Moore guest starred on The Man from U.N.C.L.E., The Rogues, My Three Sons, Peyton Place (starring Moore's then husband, Ryan O'Neal), Daniel Boone, Cowboy in Africa, and The Iron Horse. In 1967, Moore appeared as Daphne Harper, a snob and former college beauty queen chum of Darrin's, in the "Charlie Harper, Winner" episode of Bewitched. During the time, Moore also had an uncredited role as "Angie," the widow of Jesse Coe, in Nevada Smith starring Steve McQueen.
Throughout the 1950s and 1960s, Moore also made multiple appearances on The Millionaire, The United States Steel Hour, Route 66, Wagon Train, Alfred Hitchcock Presents (and The Alfred Hitchcock Hour), Hawaiian Eye, Alcoa Premiere, Gunsmoke, The Fugitive, The Virginian, High Chaparral, The F.B.I, and The Rifleman.
During the 1970s, Moore continued with guest roles on Nanny and the Professor, The Governor & J.J., and McCloud. In 1973, she appeared in the television adaption of the 1954 film Three Coins in the Fountain, also starring Yvonne Craig and Cynthia Pepper. In 1974 she appeared on The Waltons in the episode entitled "The Departure." In 1975, she co-starred in the feature film The Hindenburg. The next year, she guest-starred on Petrocelli and The Blue Knight and made two appearances on Bronk.
By the late 1970s, Moore's career had begun to wane owing to personal problems. Her only two on-screen appearances after 1976 were in a supporting role in the 1980 television film Scout's Honor starring Gary Coleman and a small bit part in the 1986 Australian film Run Chrissie Run!.
On April 3, 1963, Moore married her third husband, actor Ryan O'Neal. The couple had two children: Tatum O'Neal (b. 1963) and Griffin O'Neal (b. 1964). The marriage was tempestuous and the couple separated in early 1966. In February 1967, their divorce became final.
In February 1975, she married roofing contractor Gary L. Reeves. They divorced in 1977.
Around the time of her separation from O'Neal, Moore began to abuse alcohol and drugs, namely amphetamines, and she became addicted. She continued acting, but her depression worsened over her impending divorce.
In 1970, Moore checked into the Camarillo State Hospital for psychiatric treatment. The next year, she was arrested for drunk driving after she and O'Neal got into a fight while she and their children were visiting O'Neal's Malibu home. After her arrest, she lost custody of her children.
By the late 1970s, she was being supported financially by her daughter, Tatum, who had become an Academy Award-winning actress at age 10 and one of the highest-paid child stars of the era. The children were still in Ryan O'Neal's custody, and despite treatment Moore continued to abuse drugs and alcohol. As a result, she was arrested five times for DUI during the 1980s.
In the early 1960s, Moore became deaf as a result of otosclerosis, which her doctor said resulted from a deposit of calcium in her middle ear. Moore said that she had to read lips to understand what people were saying. An operation restored her hearing.
In 1996, Moore, a longtime smoker, was diagnosed with lung cancer. On November 22, 1997, she died from the disease at age 63. Her daughter, Tatum O'Neal, was by her side at the time of her death. Moore was initially interred at Hillside Memorial Park in Redlands, California, but her family later moved her remains to Oak Grove Cemetery in her home town of Americus, Georgia.