Three years later, she became an assistant United States attorney for the District of South Carolina.

As a federal prosecutor, she carried a diverse docket, including public corruption, RICO, drug, and fraud cases.

[2] On April 10, 2018, President Donald Trump announced his intent to nominate Lydon to serve as United States attorney for the District of South Carolina.

Lydon was the first female U.S. attorney for the District of South Carolina to be appointed by a president.

President Trump nominated Lydon to the seat vacated by Judge A. Marvin Quattlebaum Jr., who was elevated to the United States Court of Appeals for the Fourth Circuit on September 4, 2018.