Lyda Keller was born on October 16, 1892, in Keytesville, Missouri. This small town is located about 60 miles northeast of Kansas City in the central flatlands of Missouri. Not much is known about her childhood or family life in Keytesville.

Lyda married Robert Dooley on March 17, 1912. The newlyweds moved to a ranch in Twin Falls, Idaho, where they lived with Robert's brother, Ed Dooley. In 1913, they welcomed a daughter named Lorraine. Tragically, Lorraine died in 1915. Lyda claimed that Lorraine's death was due to drinking contaminated water. Later that same year, both Ed Dooley and Robert Dooley fell ill. Ed died in August 1915, and his death was ruled as ptomaine poisoning. Robert died not long after, succumbing to typhoid fever on October 12, 1915. After these events, Lyda collected life insurance money from both deaths.

In June 1917, Lyda married William G. McHaffle. Soon after their marriage, her three-year-old daughter fell ill and also died. Following this tragedy, the McHaffles moved to Montana. In October 1918, William unexpectedly grew ill and passed away from what was recorded as influenza and diphtheria.

In March 1919, Lyda married Harlen C. Lewis, an automobile salesman from Billings, Montana. However, within four months, Harlen fell sick and died due to complications from gastroenteritis.

Lyda's next marriage was to Edward F. Meyer in August 1920, in Pocatello, Idaho. Edward also fell ill soon after their wedding and died of typhoid fever on September 7, 1920.

Lyda Southard was suspected of killing multiple people to gain money from life insurance policies. Investigations began when Earl Dooley, a chemist and relative of her first husband, looked into the deaths of her family members. With the help of a doctor and another chemist, Dooley found that two of her husbands, Ed and Robert Dooley, were murdered by arsenic poisoning.

The Twin Falls County Prosecutor, Frank Stephan, directed an investigation. He ordered the exhumation of the bodies of three of Lyda's husbands, her four-year-old daughter, and her brother-in-law. Traces of arsenic were found in some of the bodies, while others showed signs that suggested poisoning. It became clear that each of her husbands had life insurance policies with her as the beneficiary, and she collected over $7,000 from the deaths.

Law enforcement discovered Lyda in Honolulu, where she had married a Navy petty officer named Paul Southard. After being extradited to Idaho, she was arraigned on murder charges. Lyda pleaded not guilty but was convicted of second-degree murder for the death of her fourth husband, Edward F. Meyer. The trial revealed that her motive was financial gain through life insurance payouts.

She was sentenced to a term of ten years to life in the Old Idaho State Penitentiary. In May 1931, Southard escaped from prison and moved to Denver, Colorado. There, she worked as a housekeeper for Harry Whitlock, whom she married in March 1932. However, he later helped authorities capture her in Topeka, Kansas, on July 31, 1932. She was returned to prison in August.

Lyda Southard was eventually released on probation in October 1941. She received a pardon before her death. Lyda passed away from a heart attack on February 5, 1958, in Salt Lake City, Utah, and was buried at Sunset Memorial Park in Twin Falls, Idaho.