William Anthony Boyle was born on December 1, 1904, in Bald Butte, Montana. This area was a gold mining camp located about two miles southwest of Marysville. His parents were James and Catherine Boyle, and the family had Irish roots. Many generations of Boyles had worked as miners in England and Scotland.

Growing up, Boyle attended public schools in both Montana and Idaho. He graduated from high school and soon began working in the mines, taking a job alongside his father. Sadly, his father passed away from tuberculosis shortly after Boyle started working. This disease is commonly linked to mining conditions.

In 1928, Boyle married Ethel Williams, and together they had a daughter named Antoinette. Early in his career, Boyle joined the United Mine Workers of America (UMWA). He quickly rose through the ranks and became the president of District 27, which covers Montana, serving in that position until 1948.

During World War II, Boyle was active in several government wartime production boards. He also served on the Montana State Unemployment Compensation Commission. In 1948, he was appointed as an assistant to the president of the UMWA, John L. Lewis. Boyle took on various roles in the union, including serving as director of UMWA District 50 and regional director of the Congress of Industrial Organizations (CIO) for four western states.

In 1960, Boyle was elected as the vice president of the UMWA. That same year, Thomas Kennedy, who had been vice president since 1947, took over as the union leader. Although Lewis preferred Boyle as his successor, Kennedy was popular among the members. As Kennedy's health declined, Boyle took over many of his responsibilities. When Kennedy became too ill to lead, Boyle was named acting president. Following Kennedy's death on January 19, 1963, Boyle was elected as president of the UMWA.

In 1969, William Anthony Boyle was involved in a significant union election for the presidency of the United Mine Workers of America (UMWA). He faced off against Joseph "Jock" Yablonski, whom Boyle had previously removed from his position in the union. The election, held on December 9, 1969, was contested, and Boyle won by a large margin. However, Yablonski questioned the fairness of the election and asked the United States Department of Labor to investigate allegations of fraud.

On December 31, 1969, Yablonski, his wife Margaret, and their daughter Charlotte were murdered in their home while they slept. The discovery of their bodies on January 5, 1970, led to a federal investigation that linked Boyle to the killings. Evidence revealed that Boyle had ordered the murders earlier that year after a heated argument with Yablonski.

In September 1969, Boyle had provided $20,000, embezzled from union funds, to an associate, Albert Pass, to hire hitmen. Pass hired three men, including Paul Gilly and two others, to carry out the murders. The plan was to delay the killing until after the election to avoid raising suspicion about Boyle's involvement.

Following the murders, the federal investigation intensified. Boyle was arrested for conspiracy to commit murder on September 6, 1973. His trial began in March 1974, and he was convicted and sentenced to three life terms in prison on April 11, 1974.

Boyle's conviction was overturned by the Pennsylvania Supreme Court on January 28, 1977, due to errors in the original trial. A new trial started on January 16, 1978. On February 18, 1978, Boyle was found guilty again of the Yablonski murders. His third appeal was denied in July 1979.

He spent the remainder of his life in prison and faced several health issues. After suffering a stroke in 1983, he died on May 31, 1985, at the age of 80, in a hospital in Wilkes-Barre, Pennsylvania.