The Trump administration's head of the Justice Department's antitrust division, who was born in Dublin, said she is stepping down less than a year after being appointed by Donald Trump.
Gail Slater was confirmed in March to head the division, which enforces laws against illegal monopolies and anti-competitive business behaviour.
She said on X it was "with great sadness and abiding hope" that she was leaving. "It was indeed the honour of a lifetime to serve in this role," she added.
Ms Slater's move throws the division into uncertainty as companies facing antitrust probes have increasingly hired Trump-connected lobbyists to influence the outcomes of their cases. It leaves the division with few senior leaders, following the departure of the division's head of civil litigation this week.
The White House referred questions on Ms Slater's departure to the DOJ.
In a statement, US Attorney General Pam Bondi said: "On behalf of the Department of Justice, we thank Gail Slater for her service to the Antitrust Division which works to protect consumers, promote affordability, and expand economic opportunity."
In July, Reuters and other outlets reported two of Ms Slater's deputies were fired for insubordination after a settlement greenlighting Hewlett Packard Enterprise's $14 billion acquisition of Juniper Networks.
The move exposed a power struggle within the Trump administration between proponents of robust antitrust enforcement and dealmakers seeking to leverage influence.
Ms Slater, who is originally from Dalkey, in Dublin, was an economic adviser to JD Vance while he was a senator, and previously worked in the White House during Mr Trump's first term.
She also worked for a decade as an antitrust lawyer at the Federal Trade Commission, where she brought cases to block mergers including Whole Foods' acquisition of organic grocer Wild Oats.
Vice President JD Vance's office declined to comment on Ms Slater's departure.
She had said her priority was to use antitrust enforcement to help Americans struggling with high living costs. The DOJ launched probes into egg producers and the meatpacking industry last year.
Her division continued the US crackdown on Big Tech companies that started during Trump's first term, with major cases against Alphabet's Google and Apple.
