The U.S. Justice Department’s Thomas Perrelli, the third-in-command under Attorney General Eric Holder Jr., is often described as a mild-­mannered consensus builder who oversees the bulk of the federal government’s civil litigation — from antitrust enforcement and civil rights litigation to environmental actions and health care fraud.

Perrelli, who joined Justice from Jenner & Block, where he managed the firm’s Washington office, has played a lead role in high-profile matters that include defending the detention of Guantánamo Bay prisoners and negotiating the $20 billion claims settlement with BP PLC after the Gulf of Mexico oil spill. Perrelli was a lead negotiator in two major class action settlements announced under Holder — Cobell v. Salazar and a case involving discrimination against black farmers.