Merrick Garland pauses federal executions a year after his predecessor resumed them.

Attorney General Merrick B. Garland on Thursday imposed a moratorium on federal executions pending a review of the Justice Department’s policies and procedures, reversing the Trump administration’s decision to resume executions of federal death row inmates last year after a nearly two-decade hiatus.

“The Department of Justice must ensure that everyone in the federal criminal justice system is not only afforded the rights guaranteed by the Constitution and laws of the United States, but is also treated fairly and humanely,” Mr. Garland said in a memo to Justice Department leaders. “That obligation has special force in capital cases.”

Mr. Garland said in his memo that the deputy attorney general, Lisa O. Monaco, would supervise a review of Justice Department policies related to federal executions that were implemented by former Attorney General William P. Barr. He asked that several of the department’s divisions, including the Bureau of Prisons, the criminal division and the civil rights division, participate, along with other federal agencies and outside advocacy groups.

After 17 years without executions, the Justice Department under Mr. Barr began to execute federal death row inmates last summer. He argued that the Justice Department under both parties had sought the death penalty and that the government owed “the victims and their families to carry forward the sentence imposed by our justice system.”

The Trump administration ultimately executed 13 people, more than three times the number of people put to death by the federal government in the previous six decades.

Andrew Bates, a White House spokesman, said President Biden approved of Mr. Garland’s decision.

“As the president has made clear, he has significant concerns about the death penalty and how it is implemented, and he believes the Department of Justice should return to its prior practice of not carrying out executions,” Mr. Bates said.

As a candidate, Mr. Biden said that he would work to abolish federal executions and incentivize states to follow suit.

The Supreme Court also said in March that it would review an appeals court’s decision to overturn the death sentence of Dzhokhar Tsarnaev, who was sentenced to death for his role in the 2013 Boston Marathon bombings.

Should the Biden administration withdraw its support for the death penalty against Mr. Tsarnaev, the Supreme Court case would become moot.

Mr. Garland has asked the department to review policies implemented in the last two years that paved the way to restart federal executions.