Known as Tony, Marshall was the only child of the American philanthropist Brooke Astor and her first husband, New Jersey state senator John Dryden Kuser. Marshall was the stepson of Charles H. Marshall (his mother's second husband, whose surname he adopted at the age of 18), and also of the American millionaire Vincent Astor (his mother's third husband).
By his father's second marriage, he had a half-sister, Suzanne Dryden Kuser (born November 24, 1931), who served with the U.S. Department of State, was an intelligence officer with the Central Intelligence Agency, and has been a consultant to the National Security Agency. He also had two stepsiblings, Peter Marshall and Helen Huntington Marshall (born April 6, 1918), wife of the composer Ernest Schelling and later of the cellist János Scholz.
Marshall attended Brooks School in North Andover, Massachusetts. After enlisting in 1942, he served with the U.S. Marine Corps and led his platoon in the battle of Iwo Jima, attaining the rank of Lieutenant and earning a Purple Heart. After the end of the war, he enrolled in Brown University.
Marshall was the U.S. consul in Istanbul, Turkey (1958–1959), then, during the Nixon administration, served as the U.S. ambassador to the Malagasy Republic (1969–1971). He was expelled by the Malagasy government in June 1971 following a Malagasy newspaper report that a secret document bearing his signature implicated him in a supposed coup d'etat against President Philibert Tsiranana.
Later he served as ambassador to Trinidad and Tobago (1972–74) and Kenya (1973); and then, during the Ford administration, to the Seychelles (1976). He was also an assistant to Richard Mervin Bissell Jr. during the development of the U-2 reconnaissance aircraft.
In the 1980s, Marshall was an officer with United States Trust Company of New York, where he assisted the bank with the management of large estate accounts.
Anthony Marshall's first production was the Tony-nominated Alice in Wonderland which he produced with Sabra Jones and WNET. He and his wife, Charlene Marshall, formed Delphi Productions in 2003 with producer David Richenthal, and they produced the Tony Award-winning Long Day's Journey into Night (Tony Award, Best Revival of a Play (2003)), and I Am My Own Wife (Tony Award, Best Play, (2004)).
Marshall was married three times. His first wife was Elizabeth Cynthia Cryan, whom he married on July 26, 1947 in Wynnewood, Pennsylvania. The groom's stepfather, Charles Marshall, was his best man. The couple had twin sons:Alexander R. Marshall (born May 14, 1953), a photographer
Philip Cryan Marshall (born May 14, 1953), a tenured professor and director of historic preservation at Roger Williams University.
His second wife was his former secretary Thelma Hoegnell (born May 11, 1928), whom he married on December 29, 1962. The couple were divorced on January 24, 1990, reportedly following Marshall's affair with Charlene Gilbert, the wife of an Episcopal priest in Northeast Harbor, Maine.
His third wife, and widow, whom he married in 1992, is the former Charlene Detwyler Tyler (born July 28, 1945), the former wife of Paul E. Gilbert, a naval officer turned Episcopal priest, and a daughter of Charles Matthew Tyler, an insurance actuary and businessman of Charleston, S.C. By this marriage Marshall had two stepdaughters, Arden (born 1969) and Inness (born 1972) and a stepson, Robert (born 1976). Charlene Marshall was tried in the press for goading her husband to loot the Astor Foundation charitable funds, but, was never formally charged.
In 2003 and 2004, changes were made to Brooke Astor's will which transferred who were some of the beneficiaries from a few of Astor's favorite institutions, like the Metropolitan Museum of Art and the New York Zoological Society, to the Anthony Marshall Fund. In February 2004, the law firm of Sullivan & Cromwell, which had represented Astor for over 50 years, was also fired, and replaced with Francis X. Morrissey Jr., an attorney friend of Marshall's who had a history of being disciplined by the New York State Bar Association.
In July 2006, Philip Marshall filed suit against his father, alleging mistreatment of his grandmother Brooke Astor and mismanagement of her funds. He requested that Anthony Marshall be dismissed as her guardian and replaced by family friend Annette de la Renta. That request was granted temporarily, pending a court hearing on August 8, 2006.
On August 1, 2006, The New York Times reported that Anthony Marshall was accused by Alice Perdue, who was employed in his mother's business office, of diverting nearly $1 million from his ailing mother's personal checking accounts into his highly successful theatrical productions. However, Mrs. Astor received a 20 percent return on her investments.
On September 7, 2006, an article in the Times revealed that J. P. Morgan Chase, the court-appointed temporary guardian of Brooke Astor’s assets, was investigating whether Marshall improperly obtained about $14 million in cash, property and stocks from his ailing mother while managing her finances. J.P. Morgan considered litigation against Marshall to get some of the money and property back. The article further suggested that Brooke Astor's mental competency was an issue in her later years, putting her property and securities transfers into question. According to an affidavit presented by J. P. Morgan Chase, “[Q]uestions have been raised as to Mrs. Astor’s competence at this point in time to participate in such transactions and therefore the extent to which Mr. Marshall alone implemented these transactions." On December 5, 2006, an independent court evaluator released a report stating that, "while specific claims of elder abuse were not proven," many of Marshall's financial dealings were suspect. Marshall was ordered to return to his mother's estate $11 million in assets, including art, jewelry given to his wife as gifts from Mrs. Astor and money. He maintained his innocence but eventually agreed in the settlement to "cede any claims to his mother's medical treatment or finances."
On November 27, 2007, Marshall surrendered to authorities at the Manhattan district attorney's office to face indictment on sixteen counts relating to the handling of Brooke Astor's will and financial affairs. The charges included conspiracy, grand larceny and possession of stolen property. Attorney Francis X. Morrissey, a longtime friend of Mrs. Astor's, was also charged with six counts including conspiracy, forgery and possession of a forged instrument.
At a press conference following Marshall's arrest, Manhattan district attorney Robert M. Morgenthau stated that "Marshall and Morrissey took advantage of Mrs. Astor’s diminished mental capacity in a scheme to defraud her and others out of millions of dollars." He further said that "Marshall abused his power of attorney and convinced Mrs. Astor to sell property by falsely telling her that she was running out of money. He is charged with stealing money from her as well as stealing valuable art work from her Park Avenue apartment."
The trial of Marshall and Morrissey started March 30, 2009, coincidentally his late mother's birthday. On October 8, 2009, Marshall was found guilty of 14 of the 16 charges, including first-degree grand larceny. Although he had his mother's Power of Attorney since the 1970's, jurors convicted him of giving himself an unauthorized raise of about $1 million for managing his mother’s finances.
On December 21, 2009, Marshall was sentenced to one to three years in prison. Marshall's attorneys appealed, citing jury tampering, but the appeal was rejected. Marshall reported to prison on June 21, 2013.
However, after serving just eight weeks of his sentence, the 89-year-old Marshall had grown so sick and frail that he was granted immediate parole on August 22, 2013. His health problems included Parkinson’s disease and congestive heart failure; his lawyers claimed he could not walk, stand, clean himself or dress himself. Marshall died on November 30, 2014 at the age of 90.