John E. Nolan Jr. with Cuban leader Fidel Castro in 1962. (Courtesy of the Nolan family)

John E. Nolan Jr., a senior partner at the Washington law firm Steptoe & Johnson, former assistant to Attorney General Robert F. Kennedy and a negotiator with Cuban leader Fidel Castro on the return of Americans captured in the 1961 Bay of Pigs invasion, died Nov. 18 at his home in Bethesda, Md. He was 90.

The cause was pneumonia, said a daughter, Patricia McNeill.

In December 1962, while in private practice with Steptoe & Johnson, Mr. Nolan was asked to join New York lawyer James B. Donovan in negotiating with Castro for the release of 1,100 men captured in the abortive Bay of Pigs invasion of Cuba in April 1961.

(Donovan was the lawyer who negotiated the 1962 exchange of downed U-2 pilot Francis Gary Powers for the Soviet spy Rudolf Abel, which was dramatized in the 2015 Steven Spielberg movie “Bridge of Spies.”)

The two lawyers met Castro during several visits to Cuba over an extended period, and Mr. Nolan facilitated the procurement of about $50 million in medical supplies in exchange for the prisoners’ release.

John E. Nolan Jr. and his wife, Joan. (Family Photo)

In a 1967 oral history interview for the John F. Kennedy Presidential Museum and Library in Boston, Mr. Nolan said Castro “was always reasonable, always easy to deal with. There were no tantrums, fits. He was a talker of very significant proportions . . . he would come over at midnight or 1 o’clock in the morning and stay all night talking. But he wasn’t a conversational hog . . . He’d ask questions, listen for answers, give his own viewpoints.”

In a separate interview with Washington Lawyer, Mr. Nolan said Castro, who died in 2016, had “a good sense of humor.” Mr. Nolan recalled he rode across Cuba with Castro to visit the Bay of Pigs and “fished on his boat while Castro told us stories about the invasion. We also went to three games of the Cuban World Series with him . . . That doesn’t mean that Castro is a friend of the United States or that Cuba is a flourishing free-speech democracy.”

Mr. Nolan took a leave from Steptoe & Johnson in 1963 to serve as an assistant to Attorney General Robert F. Kennedy. He spent much of the summer of 1963 in the Deep South, taking part in Justice Department efforts during the civil rights movement. He later worked for Kennedy’s 1964 successful senatorial campaign in New York and in his 1968 presidential bid in the months before his assassination in Los Angeles.

John Edward Nolan Jr. was born July 11, 1927, in Minneapolis. His father was an inventor and builder who later worked for the 3M manufacturing company.

Mr. Nolan graduated from the U.S. Naval Academy in 1950, choosing the Marine Corps as his branch of service. He led his rifle platoon in hand-to-hand combat during the Korean War and was awarded a Silver Star, Bronze Star and Purple Heart.

“You have the feeling that you are doing something,” Mr. Nolan told Washington Lawyer about his wartime experience. “There is a momentum to moving forward, going up hill and throwing off the enemy.”

Five decades later, Mr. Nolan “still walked with an air of authority and the bearing of a 22-year-old Marine,” said a law partner, Roger E. Warin.

Mr. Nolan enrolled at Georgetown University Law School while still serving in the Marines. For a time, he also was a U.S. Capitol Police officer working the midnight shift.

He graduated from law school in 1955, then served a year as clerk to Supreme Court Justice Tom C. Clark. He joined Steptoe & Johnson in 1956 and would continue his association with the firm until 2013.

Mr. Nolan’s specialties as a lawyer included environmental cases and the rights of whistleblowing federal employees. He represented oil companies building the Alaska pipeline in the 1970s.

He also represented whistleblower A. Ernest Fitzgerald in a lawsuit against President Richard M. Nixon after Fitzgerald reported more than $2 billion in federal cost overruns and was dismissed from his civilian job with the Air Force. Mr. Nolan reached a settlement “under circumstances that were favorable to Fitzgerald.”

In the 1990s, he was the mediator in a tangled family dispute involving multimillionaire discount retailer Herbert H. Haft, Haft’s wife, Gloria, and their children.

“There was yelling, tipping over of water pitchers,” Mr. Nolan said in his interview with Washington Lawyer, “a venting of a whole lifetime of suppressed feelings.”

At one time, Mr. Nolan was his law firm’s chief recruiter for new talent. “He’s no dancing bear,” he would say of a candidate who failed to pass muster. He received the D.C. Bar Association’s “Legends in the Law” award in 2003.

Survivors include his wife of 67 years, Joan Dobbins Nolan of Bethesda; four children, Carol N. Klatt of Buck Hills Falls, Pa., Kelly N. Spencer and Patricia N. McNeill, both of Bethesda, and Richard C. Nolan of Albany, N.Y.; and eight grandchildren. A son, John E. Nolan III, died in 1980.

In 2001, Mr. Nolan returned to Cuba for a 40th anniversary observance of the failed Bay of Pigs invasion. He had lunch with Castro twice, he said, and talked to him a few more times. The Cuban leader sent him a box of Cuban cigars.