Michael J. Kennedy

Michael J. Kennedy, who as a criminal lawyer championed lost causes and deeply unpopular defendants — including John Gotti Sr., Huey P. Newton and Timothy Leary — and finally won freedom for Jean S. Harris, the convicted killer of Dr. Herman Tarnower, the Scarsdale Diet doctor, died on Monday in Manhattan. He was 78.

The cause was complications of pneumonia, which developed while he was being treated for cancer, his wife, Eleanora, said.

A steadfast defender of the underdog and the First Amendment, Mr. Kennedy represented radicals including Rennie Davis, Bernardine Dohrn and Mr. Newton, co-founder of the Black Panther Party. His clients also included the Native American protesters at Wounded Knee, S.D., the family of the rogue real estate heir Robert A. Durst; Mr. Leary, the LSD guru; and Mr. Gotti, the mob boss.

He also represented High Times magazine from its inception (and was later an owner) and shared its agenda to decriminalize marijuana possession. As matrimonial counsel for Ivana Trump in 1991, Mr. Kennedy publicly rejected as insufficient a divorce settlement — trumpeted by her husband, Donald J. Trump — in which she was to receive more than $10 million and their Connecticut home and Manhattan apartment. The settlement was renegotiated.

Mr. Kennedy was so aggressive as a guardian of constitutional rights that he sometimes needed a lawyer himself.

In 1968, he was ejected from a congressional hearing investigating the violent demonstrations during the Democratic National Convention in Chicago. The next year he was held in contempt with three other lawyers by Judge Julius J. Hoffman for failing to appear at the trial of eight leaders of the previous summer’s protests, including Mr. Davis.

Mr. Kennedy was even the stuff of fiction. The actor Raul Julia consulted with him before playing the defense lawyer Sandy Stern in the 1990 movie version of Scott Turow’s novel “Presumed Innocent.”

Michael John Kennedy was born in Spokane, Wash., on March 23, 1937, the son of Thomas Kennedy and the former Evelyn Forbes. He was sent to a Jesuit boarding school when he was 4. He earned his bachelor’s degree from the University of California, Berkeley, and he graduated from the University of California Hastings College of the Law, in San Francisco.

His first marriage, to Pamalee Hamilton, ended in divorce. In addition to his wife, the former Eleanora Baratelli, who worked with him as a trial consultant, he is survived by their daughter, Anna Safir; two children from his first marriage, Lisa Kennedy and Scott Hamilton Kennedy, an Oscar-nominated documentary filmmaker; and five grandchildren.

Mr. Kennedy immersed himself in radical causes from the start, representing Cesar Chavez and his migrant farm workers’ union in their rent strike against California landlords who charged exorbitant rents for barely habitable shacks.

In New York, as staff counsel for the National Emergency Civil Liberties Committee, he represented conscientious objectors, draft resisters and deserters, clogging the legal system by entering not guilty pleas and demanding trials.

His clients included two Columbia University students — both of whom, he proudly pointed out, became judges — who were being disciplined for trying to shut down Columbia’s law school to protest the war in Vietnam.

In 1980 he negotiated the surrender of Ms. Dohrn, the Weather Underground leader, after she eluded the law for more than 10 years. Federal charges against her had been dropped. She pleaded guilty to aggravated battery and bail jumping stemming from violent antiwar protests and was fined $1,500 and placed on probation for three years.

In 1982, Mr. Kennedy persuaded a Brooklyn jury weighing charges against five men accused of conspiring to smuggle weapons to the Irish Republican Army that the Central Intelligence Agency had sanctioned their gunrunning.

“It is up to the government to prove that the C.I.A. was not involved with the defendants,” Mr. Kennedy declared, “not our burden to prove that it was.”

In 1993 he persuaded Gov. Mario M. Cuomo to grant clemency to Mrs. Harris, the former private school headmistress who in 1980 killed Dr. Tarnower in what she said was a botched suicide attempt but which prosecutors proved was vengeance by a woman scorned. She had suffered at least two heart attacks in prison.

And the following year, he stunned fellow lawyers by arranging for his client, Ricardo S. Caputo, to explain in a television interview — before he surrendered to the police — why he had killed several women. The tactic apparently helped spare him the death penalty.

Speaking of Mr. Tigar, Mr. Kennedy might just as well have been referring to himself when he said in 1995: “He understands that the way we measure the value of our justice system is how it treats society’s pariahs. It’s easy to treat the popular people well.”