Born in London in 1923, he was the only child of Lieutenant General Sir Sydney Turing Barlow Lawford, KBE (1865–1953) and May Sommerville Bunny (1883–1972). At the time of Peter's birth, however, his mother was married to Capt Dr Ernest Vaughn Aylen, one of Sir Sydney's officers, while his father was married to Muriel Williams. At the time, May and Ernest Aylen were living apart. May confessed to Aylen that the child was not his, a revelation that resulted in a double divorce. Sydney and May wed in September 1924 after their divorces were finalised and when their son was one year old.
He spent his early childhood in France and, owing to his family's travels, was never formally educated. Instead, he was schooled by governesses and tutors, and his education included tennis and ballet lessons. "In the beginning," his mother observed, "he had no homework. When he was older he had Spanish, German and music added to his studies. He read only selected books: English fairy stories, English and French classics; no crime stories. Having studied Peter for so long, I decided he was quite unfitted for any career except art, so I cut Latin, Algebra, high mathematics and substituted dramatics instead." Because of the widely varying national and religious backgrounds of his tutors, Lawford "attended various services in churches, cathedrals, synagogues and for some time was an usher in a Christian Science Sunday School...." Around 1930, aged seven, he made his acting debut in the English film Poor Old Bill.
Prior to the Second World War, Lawford was offered a contract by Metro-Goldwyn-Mayer. In 1938, he made his Hollywood debut in a minor part in the film Lord Jeff. His first role in a major film production was in A Yank at Eton (1942), starring Mickey Rooney, in which Lawford played a snobbish bully. He had uncredited roles as a pilot in Mrs. Miniver (1942) and as a Sailor in Sherlock Holmes Faces Death (1943).
He was a member of the "Rat Pack" and brother-in-law to President John F. Kennedy. From the 1940s to the 1960s, he was a well-known Celebrity and starred in a number of highly acclaimed films. In later years, he was noted more for his off-screen activities as a Celebrity than for his acting; it was said that he was "famous for being famous".
In June 1943, MGM signed Lawford to a long-term contract. His first role under this was The White Cliffs of Dover (1944), in which he played a young soldier during the Second World War. MGM gave him another important role in The Picture of Dorian Gray (1945). Lawford's first leading role came in Son of Lassie (1945), and he later won a Modern Screen magazine readers' poll as the most popular actor in Hollywood of 1946. His fan mail jumped to thousands of letters a week.
With actors such as Clark Gable and James Stewart away at war, Lawford was recognised as a new romantic lead on the MGM lot. Lawford's busiest year as an actor was 1946, when two of his films opened within days of each other: Cluny Brown and Two Sisters from Boston. He made his first comedy film that year, My Brother Talks to Horses (released in 1947). He appeared with Frank Sinatra for the first time in the musical It Happened in Brooklyn (1947). Lawford received rave reviews for his work in the film, while Sinatra's were lukewarm.
Lawford later admitted that the most terrifying experience of his career was the first musical number he performed in the musical Good News (1947). Using an American accent for his role, he won acclaim as a performer. Over the next few years, he was given supporting roles in MGM films, including On an Island with You (1948), Easter Parade (1948), Little Women (1949), Royal Wedding (1951) and You for Me (1952).
Lawford made his television debut in 1953 in a guest-starring role on Ronald Reagan's anthology series General Electric Theater. In 1954, he starred as a newspaper advice-to-the-lovelorn columnist named Bill Hastings in the short-lived NBC series Dear Phoebe with Marcia Henderson and Charles Lane.
His first marriage, in 1954, was to socialite Pat Kennedy, a younger sister of then-US Senator John F. Kennedy (D-MA). They had four children: a son, actor and author Christopher Kennedy Lawford (b. 1955), and daughters Sydney Maleia Lawford (b. 1956), Victoria Francis Lawford (b. 1958), and Robin Elizabeth Lawford (b. 1961).
From 1957 to 1959, Lawford co-starred with Phyllis Kirk in The Thin Man, an NBC series from MGM based on the novel by Dashiell Hammett. He had a recurring role on The Doris Day Show from 1971 to 1973 as the love interest to Day's character.
Lawford's first film after Metro released him and several other players from their contracts was the comedy It Should Happen to You, wherein he starred alongside Judy Holliday and Jack Lemmon. In 1959, Sinatra invited Lawford to join the "Rat Pack" and also got him a role in Never So Few. The casino caper Ocean's 11 (1960) was a project Lawford first brought to Sinatra's attention. Other films included the acclaimed Israeli-set drama Exodus (1960); The Longest Day (1962), a war film with a star-studded cast; and the political drama Advise & Consent (1962) (in which he played a United States Senator). He reunited with the Rat Pack for the western adventure Sergeants 3.
Lawford became an American citizen on 23 April 1960. He had prepared for this in time to vote for his brother-in-law in the upcoming presidential election. Lawford, along with other members of the "Rat Pack", helped campaign for Kennedy and the Democratic Party. Sinatra famously dubbed him "Brother-in-Lawford" at this time. Lawford and Patricia Kennedy divorced in February 1966.
In 1961, Lawford and his manager Milt Ebbins formed Chrislaw Productions, which was named after Peter's son Christopher, and produced the 1963 action film Johnny Cool starring Henry Silva and Elizabeth Montgomery. He went on to produce the 1965 Patty Duke film Billie as well as two films with Sammy Davis, Jr., Salt and Pepper and One More Time. He returned to MGM for They Only Kill Their Masters (1972), which reunited him with several former MGM contract players. His last role was as Montague Chippendale in Where Is Parsifal? (1983).
Lawford was originally cast as Alan A. Dale in the film Robin and the 7 Hoods but was replaced by Bing Crosby following a break in Sinatra's relationship with Lawford. The break stemmed from a scheduled visit to Sinatra's home by Lawford's brother-in-law, President Kennedy, during a 1962 West Coast trip. Attorney General Robert F. Kennedy, who was long concerned about Sinatra's rumoured ties with underworld figures, encouraged the President to change his plans and stay at Crosby's home, which (it was maintained) could provide better security for the President. The change came at the last minute, after Sinatra had made extensive arrangements for the promised and eagerly awaited presidential visit, including the construction of a helipad. Sinatra was furious, believing that Lawford had failed to intercede with the Kennedys on his behalf, and ostracised him from the Rat Pack.
Sinatra and Lawford's friendship was over. They only spoke when Sinatra called after his son Frank Sinatra Jr. was kidnapped on 8 December 1963, and he needed the help of Lawford's brother-in-law Robert Kennedy, then Attorney General. With the exception of Vice-President Hubert H. Humphrey's 1968 presidential race, Sinatra never endorsed another Democratic candidate. Ironically, Crosby, a staunch Republican, ended up cast in Lawford's role.
Lawford married his second wife, Mary Rowan, daughter of Comedian Dan Rowan, in October 1971 when she was one day shy of her 22nd birthday; Lawford was 48. Rowan and Lawford separated two years later and divorced in January 1975. In June 1976, at age 52, he married aspiring Actress Deborah Gould, 25, whom he had known for only three weeks. Lawford and Gould separated two months after marrying and divorced in 1977. During his separation from Gould, Lawford met 18-year-old Patricia Seaton—a woman more than 40 years his junior—who became his fourth and final wife in July 1984, just months before his death.
Lawford died at Cedars-Sinai Medical Center in Los Angeles on Christmas Eve 1984, aged 61, from cardiac arrest. He had suffered from kidney and liver failure after years of substance abuse. His body was cremated, and his ashes were interred at Westwood Village Memorial Park Cemetery. Owing to a dispute between his widow and the cemetery, Lawford's ashes were removed from the cemetery in 1988 and scattered into the Pacific Ocean off the coast of California by his widow Patricia Seaton Lawford, who invited the National Enquirer tabloid to photograph the event.
Lawford's family was connected to the English aristocracy through his uncle Ernest Lawford's wife (a daughter of the 14th Earl of Eglinton) as well as his aunt Ethel Turner Lawford (who married a son of the 1st Baron Avebury). His aunt, Jessie Bruce Lawford, another of his father's sisters, was the second wife of the Hon Hartley Williams, senior puisne judge of the Supreme Court of the colony of Victoria, Australia. A relative, through his mother, was Australian Artist Rupert Bunny.