Barlow said he was announcing his departure early to give President Barack Obama and Sens. Orrin Hatch and Mike Lee time to begin the process of selecting a new U.S. attorney for Utah.
Barlow's tenure was praised by former federal prosecutors, including Brett Tolman, who held Barlow's job from 2006 to the end of 2009.
"David, I think, was a good steward of the office," Tolman said. "He worked hard and I know he was well-liked so I think it's unfortunate he's moving on."
Brent Baker, a former special assistant U.S. attorney in Utah, also said Barlow was respected within the office.
"I truly hear from all corners that he has done a great job," Baker said.
But Tolman and Baker both expressed concerns that the quick turnover was not good for Utah. The post had been vacant of a presidential appointee from Tolman's departure to Barlow taking office in the latter part of 2011.
"We need someone who will stay in the position for five years or eight years," Baker said, "whatever it takes through whatever administrations come and go so they can implement whatever their strategic plan is."
U.S. Attorney General Eric Holder called Barlow "a fierce advocate for the people of Utah" and praised his work as a member of the U.S. Attorneys Advisory Committee and as chair of the Justice Department's Local Government Coordination Working Group.
"Although I will miss his contributions to the Justice Department's mission," Holder said in a statement, "I am confident that the impact of his efforts will continue to be felt for some time."
Barlow originally joined Sidley Austin in 2000 and became a partner in 2006. He became legal counsel to Lee after the Utah Republican won election to the Senate in 2010.
Obama tapped Barlow to become U.S. attorney for Utah in August 2011 after the post had been vacant for almost two years and at least two candidates had been rejected or withdrawn, including Baker. The Democratic president's decision to appoint the chief counsel for the Republican Lee angered Utah Democrats.
Barlow is returning to Sidley Austin as a partner in the Washington, D.C., office to focus on clients in the life sciences area, the firm said.
Barlow's tenure has been marked by several high-profile cases, including that of Jeremy Johnson, the St. George businessman whose accusations of political corruption sparked political and legal investigations and led to the resignation of Utah Attorney General John Swallow.
Barlow's office began an investigation of Swallow but withdrew without explanation, turning the case over to the Public Integrity Section of the Department of Justice, which later said it would not pursue charges.
Barlow was personally involved in the indictment of Fazliddin Kurbanov, an Uzbekistan national indicted last year on federal terrorism charges, according to Barlow's office. He also has been involved in the prosecution of Roberto Miramontes Roman in the death of Millard County Deputy Sheriff Josie Greathouse Fox.
Barlow was a member of the trial teams in three cases, including a child-pornography prosecution and a fraud prosecution involving the Paiute Nation.