WASHINGTON—The Justice Department is examining allegations that Corey Lewandowski profited off his top position at the Department of Homeland Security, people familiar with the matter said.

The inquiry is based on a referral from the DHS inspector general, which shared its findings about Lewandowski’s tenure at the department in recent days, the people said.

The review is the first publicly known instance of Trump’s second-term Justice Department scrutinizing someone close to the president.

Lewandowski served as the top adviser to then-Homeland Security Secretary Kristi Noem up until the pair were ousted from the department in March, following increasingly embarrassing revelations about the infighting at the agency and their spending decisions.

While at the department, Lewandowski appeared to try to use his vast influence for personal financial gain, including asking several countries in the Middle East to hire him on the side to assist with visa issues and other matters, The Wall Street Journal has previously reported.

He or close associates signed off on nearly all department spending decisions for amounts exceeding $100,000, giving Lewandowski visibility into the array of contractors DHS worked with, and the ability to hold the contracts up.

Lewandowski has previously denied seeking foreign contracts while in government or playing a role in approving DHS contracts.

A representative for Lewandowski said Lewandowski hasn’t been contacted by the Justice Department regarding any investigation. “He denies any wrongdoing when he was proudly serving his country in a voluntary capacity,” the representative said. The DHS inspector general’s office said it doesn’t discuss specific investigative matters or confirm or deny the existence of an investigation.

Since Trump took office last year, Justice Department officials have largely focused on trying to build cases against many of Trump’s political adversaries and other favored targets—and have dropped cases involving people with ties to the administration.

More broadly, the Justice Department has curtailed efforts to pursue cases of fraud and corruption against public officials, amid criticism from Trump and others in the administration who say such prosecutions weaponize the justice system for political ends. A unit that focused on such investigations is down to two prosecutors, after roughly two dozen others left the department or were transferred to other roles.

Investigators with the DHS inspector general’s office found evidence that Lewandowski may have been involved in improperly awarding government contracts, the Journal reported in July. The office, the agency’s internal watchdog, had for months been weighing a criminal referral to the Justice Department.

The current Homeland Security secretary, Markwayne Mullin, has received briefings on the investigation, according to people familiar with the matter.

The investigators looked into many of the contracts the department signed during Noem’s tenure, and department officials had been surprised at how involved Lewandowski was in the contracting process, some of the people said. He personally signed specific contracts, according to people who reviewed those documents or had knowledge of the approvals, despite not technically serving as a full-time U.S. government official.

He was working in an unpaid capacity as a “Special Government Employee,” a designation in federal ethics law meant to bring outside officials with particular expertise into the government on a temporary and part-time basis, without forcing them to relinquish outside work or investments.

Lewandowski served as Trump’s first campaign manager in 2016 and has maintained a close relationship over the years with the president, who valued his loyalty.

Lewandowski has told people close to him he expects the president would pardon him in the event of a criminal case, the Journal previously reported. A lawyer for Lewandowski has said Lewandowski didn’t speak about or suggest that he would seek or need a presidential pardon.