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.

The Cobell litigation, which spanned more than 15 years, recently ended in approval of a record $3.4 billion settlement. Senior Judge Thomas Hogan of Washington federal district court thanked Perrelli for his dedication to resolving the dispute.

In an interview, Perrelli said he approaches big cases with the belief “that a resolution is possible if we all sit down and work through our interests and issues to find a place that will be beneficial to everyone.”

Perrelli also oversees the grantmaking program at Justice that invests nearly $3 billion in state, local and tribal law enforcement. Wilmer Cutler Pickering Hale and Dorr partner David Ogden, a former deputy attorney general in the Holder front office, said Perrelli “really cares about the department’s missions to protect regular people from crime and other violations of their rights, and to serve and protect the interests of the country.” — Mike Scarcella