Mitchell was pronounced dead at 6:29 p.m. EDT at the U.S. Penitentiary, Terre Haute, according to a statement from U.S. Department of Justice spokeswoman Kerri Kupec. He was given an injection of pentobarbital.
Mitchell was sentenced to death after confessing that he and an accomplice had killed a 63-year-old woman and her 9-year-old granddaughter on the Navajo reservation in 2001, according to the DOJ.
"Nearly 19 years after Lezmond Mitchell brutally ended the lives of two people, destroying the lives of many others, justice finally has been served," Kupec said in the statement.
The father of the murdered girl and other Navajo Nation members belonging to the victims' families were present at Mitchell's execution, the statement said.
Attorneys for Mitchell said in a statement Wednesday that with the execution, "the federal government added another chapter to its long history of injustices against Native American people."
"Over the steadfast objection of the Navajo Nation, and despite urgent pleas for clemency from Navajo leaders and many other Native American tribes, organizations, and citizens, the Trump Administration executed Lezmond Mitchell, a Navajo man, for a crime against other Navajo people committed on Navajo land," deputy federal public defenders Jonathan Aminoff and Celeste Bacchi said in a joint statement Wednesday.
The attorneys said the execution "represents a gross insult to the sovereignty of the Navajo Nation," and added that there was "little doubt" that racial bias on Mitchell's jury, which had 11 white members and one Navajo member, had affected the case. In 2003, the federal jury found Mitchell guilty of numerous offenses and recommended the death penalty, which the court imposed.
Mitchell failed to receive a commutation of his sentence to life imprisonment from President Donald Trump and was denied a stay of his execution by the U.S. Supreme Court on Tuesday night.
Navajo Nation President Jonathan Nez and Vice President Myron Lizer had supported Mitchell's petition to Trump in a July 31 letter, saying the tribe "has not opted-in for the death penalty" under the Federal Death Penalty Act and "we strongly hold to our cultural, traditional, and religious beliefs that life is sacred."
Mitchell had sought to reopen his case at the Supreme Court in light of its 2017 decision in Peña-Rodriguez v. Colorado
. That ruling supported his position that Arizona district court rules can't bar him from interviewing the jury over concerns of racial bias, Mitchell said.But Tuesday's denial did not mention Peña-Rodriguez, focusing instead on a provision of the Federal Death Penalty Act that states the federal government has to implement death sentences "in the manner prescribed by the law of the state in which the sentence is imposed."
"Considerable uncertainty exists about the scope of this provision," Justice Sonia Sotomayor wrote in a two-page statement Tuesday accompanying the court's denial of a stay. However, "because these questions are not adequately presented for our review in the pending case, I agree with this court's decision to deny a stay," Justice Sotomayor said.
Mitchell had separately alleged before the Ninth Circuit that his execution warrant violated the Federal Death Penalty Act. His motion to the Supreme Court briefly mentioned the Ninth Circuit litigation as additional grounds for a stay.
But Justice Sotomayor said Tuesday that Mitchell's point of contention with the FDPA "does not turn on the question most in need of this court's guidance: whether the 'manner prescribed by the law of the State' includes procedures set forth in a state agency's execution protocol."
"The importance of clarifying the FDPA's meaning remains," Justice Sotomayor added. "I believe that this court should address this issue in an appropriate case."
Also on Tuesday, Mitchell filed a complaint in D.C. federal court to halt his execution while his clemency application to Trump was still pending. But the court denied Mitchell's request for a temporary restraining order early Wednesday.
Mitchell argued in the D.C. complaint that "by setting an execution date with such a shortened timeline, the Department of Justice has severely impeded the president's ability to conduct his own deliberative process ... thereby depriving Mitchell of basic procedural safeguards."
Mitchell is represented by Chuauhtemoc Ortega, Celeste Bacchi and Jonathan C. Aminoff of the Federal Public Defender's Office for the Central District of California.
The federal government is represented by Jeffrey B. Wall, Brian C. Rabbitt and Jenny C. Ellickson of the U.S. Department of Justice.
The case is Lezmond Charles Mitchell v. U.S., case number 20-5398, in the U.S. Supreme Court.
--Editing by Katherine Rautenberg and Jill Coffey.
Update: This story has been updated with comment from Mitchell's lawyers and the Department of Justice.