Thomas S. Williamson Jr. (Covington & Burling/Covington & Burling)

Thomas S. Williamson Jr., a labor and employment lawyer who served as solicitor for the Labor Department and helped devise the NFL’s “Rooney Rule” to encourage greater diversity in the hiring of coaches, died Feb. 24 at his home in Washington. He was 70.

The cause was pancreatic cancer, said his wife, Shelley Brazier.

Mr. Williamson was a longtime partner and later senior counsel at the Washington law firm of Covington & Burling, where he led the employment practice group. His work included whistleblower and job discrimination cases and negotiating agreements with the Labor Department.

Throughout his career, Mr. Williamson occasionally left the firm for pro bono work, including a year as a staff attorney for the Neighborhood Legal Services Program in 1976. He was deputy inspector general for the U.S. Department of Energy from 1978 to 1981 and, from 1993 to 1996, was the Labor Department’s solicitor, or chief legal officer, supervising a staff of 700, including 500 lawyers.

In 2003, when Mr. Williamson was a special adviser to the National Football League, he had a key role in establishing a new leaguewide rule encouraging owners to include minority candidates for head-coaching openings. It became known as the Rooney Rule after Dan Rooney, the principal owner of the Pittsburgh Steelers and chairman of the owners’ diversity committee.

More recently, Mr. Williamson led a legal team defending the same-sex marriage law in the District of Columbia. He also worked on a nationwide class-action lawsuit requiring the U.S. Postal Service to improve American Sign Language interpreter services for its deaf employees.

In 2008, Mr. Williamson was one of two partners at Covington & Burling named by the National Law Journal among “The 50 Most Influential Minority Lawyers in America.” Another was Eric H. Holder Jr., who served as U.S. attorney general under President Barack Obama.

Thomas Samuel Williamson Jr. was born July 14, 1946, in Plainfield, N.J. His father, an Army lieutenant colonel, was among the military’s first African American officers placed in command of white troops.

Mr. Williamson grew up in Piedmont, Calif., and turned down an athletic scholarship to Stanford University to attend Harvard University, where he was an all-Ivy League defensive back on the football team. One of his teammates was the actor Tommy Lee Jones.

Mr. Williamson graduated magna cum laude from Harvard in 1968 and was elected to the Phi Beta Kappa honor society. He attended the University of Oxford in England on a Rhodes scholarship, then spent a year in Ethi­o­pia training U.S. Peace Corps volunteers for an Ethio­pian company.

He was a 1974 graduate of Boalt Hall, the law school of the University of California at Berkeley. He joined Covington & Burling shortly after graduation and became a partner of the firm in 1982.

Mr. Williamson was a past president of the D.C. Bar and a past co-chair of the Lawyers’ Committee for Civil Rights Under Law.

His marriage to Rahel Haile ended in divorce. Survivors include his wife of 28 years, Shelley Brazier of Washington; three children from his second marriage, Thomas S. Williamson III and Taylor Williamson, both of Los Angeles, and Christopher Williamson of Wausau, Wis.; a daughter from another relationship, Kai Williamson of Atlanta; his mother, Winifred Williamson of Piedmont; and a sister.