Kelly Gissendaner, the only woman on Georgia's death row, was executed early Wednesday, authorities said.
The execution came after Georgia's Supreme Court, the U.S. Supreme Court and a federal appeals court all denied requests for a stay of execution.
Gissendaner, who was convicted of orchestrating her husband's murder almost 20 years ago, died by lethal injection at 12:21 a.m. Wednesday.
Last-minute appeals had been filed to the U.S. Supreme Court, the Eleventh Circuit Court of Appeals and that state Supreme Court, all of which rejected her motions. In a 5-to-2 decision, the state Supreme Court denied Gissendaner's motion for stay of execution and dismissed her constitutional challenge of her sentence as "disproportionate."
Earlier Tuesday, a letter sent to the Georgia State Board of Pardons and Parolees on behalf of Pope Francis asked for Gissendaner to not be executed.
The letter, obtained by ABC News, was signed by Archbishop Carlo Maria Vigano and addressed to members of the board. It cited the pope's speech to Congress, in which Francis said "every life is sacred," and that "society can only benefit from the rehabilitation of those convicted of crimes."
The letter asked for a sentence that "would better express both justice and mercy."
"Please be assured of my prayers as you consider this request by Pope Francis for what I believe would be a just act of clemency," the letter said.
Gissendaner was accused of convincing her boyfriend, Gregory Owen, to kill her husband, Douglas Gissendaner, in February 1997.
Owen and Kelly Gissendaner discussed killing Douglas Gissendaner "on four or five occasions, all at [Kelly] Gissendaner's initiation, before reaching a final agreement to kill him," according to Georgia's Attorney General's office.
"It was agreed that, on Feb. 7, 1997, while [Kelly] Gissendaner was out with friends, co-defendant Owen would kill Douglas. The murder went exactly as Gissendaner planned," the office of the Attorney General said.
Owen hit Douglas Gissendaner on the back of the head and then stabbed him in the neck eight to ten times, according to the Attorney General's Office.
Gissendaner was convicted of malice murder in 1998.