Mr. Lawford’s parents were Peter Lawford and Patricia Kennedy Lawford, who was the sister of President John F. Kennedy, Sen. Robert F. Kennedy (D-N.Y.) and Sen. Edward M. Kennedy (D-Mass.).
His father, a popular film actor in the 1940s and 1950s, was a member of the Rat Pack with Frank Sinatra, Dean Martin, Sammy Davis Jr. and Joey Bishop. Mr. Lawford grew up in Hollywood, surrounded by glamour, fame and temptation.
“I was given wealth, power and fame when I drew my first breath,” he wrote in his best-selling 2005 memoir, “Symptoms of Withdrawal.”
In his book, he wrote that Marilyn Monroe taught him how to dance the Twist. He sat on Sinatra’s knee and recalled that Judy Garland came to his family’s house to play poker.
He also wrote that he once received a gift of scrimshaw — a carved whale’s tooth — from President Kennedy at the Kennedy family’s winter home in Palm Beach, Fla. He acted as something of an older brother to the president’s only son, John F. Kennedy Jr.
Christopher Kennedy Lawford was born March 29, 1955, in Santa Monica, Calif. He was 8 when John F. Kennedy was assassinated in 1963 and 13 when Robert F. Kennedy was killed five years later.
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Both of Mr. Lawford’s parents struggled with addiction, before and after their divorce in 1966, and he said he began using drugs in his early teens. He was addicted to heroin for a time and in 1980 was arrested in Colorado for impersonating a doctor in an effort to obtain prescription drugs.
“Opiates were my drug of choice,” he wrote in his memoir, “but whatever changed my consciousness was my friend.”
In spite of his heavy drug use, Mr. Lawford graduated in 1977 from Tufts University in Massachusetts and in 1983 received a law degree from Boston College.
His father died in 1984 at age 61, after years of drug and alcohol abuse. The same year, Mr. Lawford’s 28-year-old cousin David Kennedy, one of Robert Kennedy’s sons, died of a drug overdose. The two were particularly close.
Mr. Lawford gave credit to his aunt Joan Kennedy — Teddy Kennedy’s first wife — for introducing him to an addiction treatment program in 1986.
“Joan did for me what no doctor, therapist, priest, or guru could do,” he told the Palm Beach Post in 2006. “She brought me to a church basement full of a diverse group of apparent losers who would teach me how to live without drugs and alcohol a day at a time, and a whole lot more.”
In the late 1980s, Mr. Lawford — who bore a striking resemblance to his father — embarked on an acting career. He acted in dozens of films and television shows, including the TV soap operas “All My Children” and “General Hospital.” He had small roles in such films as “The Russia House,” a 1990 spy thriller with Sean Connery and Michelle Pfeiffer, Oliver Stone’s 1991 rock-music film “The Doors,” and the 2005 motorcycle-racing film “The World’s Fastest Indian,” opposite Anthony Hopkins.
He also played a Navy officer in “Thirteen Days,” a 2000 film about the Cuban missile crisis, the real-life drama in which John F. Kennedy averted a nuclear war with the Soviet Union in 1962.
In addition to his 2005 memoir, Mr. Lawford published other books on addiction and recovery, as well as a book on hepatitis C, which he acquired through intravenous drug use.
“There are many days when I wish I could take back and use my youth more appropriately,” Mr. Lawford told the Associated Press in 2005. “But all of that got me here. I can’t ask for some of my life to be changed and still extract the understanding and the life that I have today.”
He studied counseling at Harvard University and lectured on addiction at Harvard, Columbia University and other college campuses. He spoke out on recovery issues for the White House Office of National Drug Control Policy under President Barack Obama and for the Caron Foundation, a nationwide drug and alcohol rehabilitation network.
Patrick Kennedy, the former congressman who is now an advocate for mental health and addiction recovery, wrote in a tweet, “He gave me strength and inspiration to take that first step, that leap of faith — and join him on the road to recovery in a new life of sobriety that I never thought possible.”
Mr. Lawford’s marriages to Jeannie Olsson and actress Lana Antonova ended in divorce. Survivors include his wife since 2014, Mercedes Miller, a yoga instructor; three children from his first marriage; and three sisters.
Mr. Lawford said his childhood taught him not to have any illusions about the lives and troubles of the Hollywood stars he grew up around.
“We can re-create the days when Frank, Dean, Sammy and my dad were together,” he told the Boston Globe in 2005. “But they all ended up dysfunctional, messed-up guys. And they once had everything. Money. Good looks. Success. Yet at the end, they were miserable, miserable men alone, angry, drinking. So what’s that all about?”
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