WASHINGTON — Pete Buttigieg on Tuesday released the names of nine clients, ranging from Blue Cross Blue Shield of Michigan to the retail giant Best Buy, that he advised while employed as a management consultant at McKinsey & Company, a period of his life that has come under increasing scrutiny in recent weeks.

Mr. Buttigieg’s client list also included some nonprofits, like the Natural Resources Defense Council, as well as several federal agencies.

Mr. Buttigieg was responding to pressure that had built in recent days over his work in his post-college years, which had begun to dominate the discussion surrounding his campaign and become fodder for opponents, notably Senator Elizabeth Warren of Massachusetts, who questioned why he had kept his client list secret.

Mr. Buttigieg, the mayor of South Bend, Ind., put out the client list one day after the firm announced that it would release him from a nondisclosure agreement he signed while working at McKinsey during his first three years after finishing his education.

The client list includes:

• Blue Cross Blue Shield of Michigan

• Best Buy

• The Natural Resources Defense Council

• The Environmental Protection Agency

• The United States Department of Energy

• The United States Postal Service

• The United States Department of Defense

• The Energy Foundation

• Loblaws, a Canadian supermarket chain

“Voters can see for themselves that my work amounted to mostly research and analysis,” Mr. Buttigieg said in a statement released by his campaign Tuesday. “They can also see that I value both transparency and keeping my word.”

The variety of clients on the list shows Mr. Buttigieg worked on projects in the health care and retail industries, along with federal government projects relating to the environment and the economies in Iraq and Afghanistan, as well as nonprofit environmental groups.

The list is likely to provide ammunition to those in the liberal wing of the Democratic Party who have sought to tag Mr. Buttigieg with the pejorative “Wall Street Pete” and argued that his “Medicare for all who want it” health care proposal, which would preserve private health insurance, is a sop to the insurance companies.

While Mr. Buttigieg has for years spoken about his efforts while working at McKinsey to foster economic opportunity in Iraq and Afghanistan, and wrote in his memoir this year about a project on Canadian cereal prices, the most politically troubling element of his client list might be his tenure working for Blue Cross Blue Shield of Michigan, a health care firm that at the time was in the process of reducing its work force.

Last week Mr. Buttigieg’s campaign said his time in Michigan included “analytical work as part of a team identifying savings in administration and overhead costs.” While it was not yet clear exactly what Mr. Buttigieg did at Blue Cross, his work appeared to come at about the same time the insurer announced that it would cut up to 1,000 jobs — or nearly 10 percent of its work force — and request rate increases.

The decision, announced in January 2009, came after the health insurance provider reported a loss of about $140 million primarily related to health care plans purchased by individuals. The company also announced that it was freezing pay for nonunion workers and cutting discretionary spending by 25 percent. In an interview published Tuesday by The Atlantic, Mr. Buttigieg said he was taken off the Blue Cross project in 2007, well before the layoffs were announced.

But when he was running for mayor of South Bend in 2011, Mr. Buttigieg seemed to refer to his tenure at Blue Cross as evidence that he had the skills necessary “to reimagine our budget from the bottom up.”

“One of the things I did for a living was just that,” Mr. Buttigieg said during a candidate forum. “So I remember one client organization that was a large insurance firm that had grown in such a way that there was a great deal of duplication and some people didn’t even know what the people working for them were doing.”

Mr. Buttigieg told the Atlantic on Tuesday that he was not in a position to give advice to Blue Cross. “Mostly I was with fellow consultants in a room working on a spreadsheet,” he said.

The list of Buttigieg clients also included the United States Postal Service, which had called in McKinsey in an effort to stem growing losses in its revenues as use of the mail declined.

A report prepared by McKinsey in 2010 suggested that the Postal Service cut costs by replacing career employees with other workers and reduce benefits to bring them more in line with the private sector.

Mr. Buttigieg’s Afghanistan work was done as the United States was spending millions in an effort to boost the country’s economy. Must of that work focused on looking for ways to extract and market Afghanistan’s rich natural resources, including huge veins of iron, copper, cobalt, gold and industrial metals like lithium.

But the overall project drew heavy criticism, and a former Pentagon official quipped during a Senate hearing in 2016 that at least part of McKinsey’s work had been lost.

“In my experience with McKinsey, it is a 10-page slide deck, so I am not sure it is going to answer many questions anyway,” said Brian McKeon, a deputy under secretary of defense.

The push for Mr. Buttigieg to release his client list, which aides to his presidential campaign rivals have whispered about for months, became amplified in the media in the last week following revelations that McKinsey has worked to assist the Trump administration put in place its immigration policy, which is loathed by Democrats.

The disclosure comes as Mr. Buttigieg has surged ahead in some of the latest public polls of Iowa Democrats, whose caucuses will kick off the presidential nominating calendar on Feb. 3. It is the latest in a dizzying series of disclosures his campaign has made in the name of transparency.

Under pressure from Ms. Warren, who is weeks into a rhetorical battle with Mr. Buttigieg in Iowa, Mr. Buttigieg on Monday agreed to allow reporters into his high-dollar fund-raising events and to disclose a list of his campaign’s financial bundlers. The first of those open-to-the-press fund-raising events was scheduled for Tuesday night in New York.

Ms. Warren, who does not hold closed-door fund-raising events, had criticized Mr. Buttigieg for being part of a system that “creates conflicts every single day when candidates for president sell access to their time to the highest bidder.”

Mr. Buttigieg had previously accused Ms. Warren of being “evasive” about her health care proposal and of hiding income she earned representing corporate law clients while she was a professor at Harvard University and other schools.

Ms. Warren ultimately did release a detailed health care proposal and said Sunday that she had earned $1.9 million over 30 years representing corporate clients, a fraction of what she could have made as a professor at elite law schools.

Mr. Buttigieg, 37, said last week that he had asked McKinsey to free him from a nondisclosure agreement he signed while a firm employee. On Monday, McKinsey announced that it would allow Mr. Buttigieg to reveal his clients, though he remains forbidden from discussing “confidential, proprietary or classified information obtained during the course of that work.”

“We recognize the unique circumstances presented by a presidential campaign,” a McKinsey spokesman said.