Ramsey Clark, who championed civil rights and liberties as attorney general in the Johnson administration, then devoted much of the rest of his life to defending unpopular causes and infamous people, including Saddam Hussein and others accused of war crimes, died on Friday at his home in Manhattan. He was 93.

His niece Sharon Welch announced the death.

In becoming the nation’s top law enforcement official, Mr. Clark was part of an extraordinary father-and-son trade-off in the federal halls of power. His appointment prompted his father, Justice Tom C. Clark, to resign from the United States Supreme Court to avoid the appearance of any conflict of interest involving cases in which the federal government might come before that bench.

To fill Justice Clark’s seat, President Lyndon B. Johnson appointed Thurgood Marshall, who became the first African-American to serve on the Supreme Court.

Mr. Clark, a tall, rangy man who shunned a government limousine in favor of his own beat-up Oldsmobile, set an ambitiously liberal course as attorney general. Days after taking office, he filed the first lawsuit to force a school district — Dale County, Ala. — to desegregate or else lose its federal school aid. He went on to file the first voting rights and school desegregation suits in the North.

Under the limited laws then available, Mr. Clark sued to prevent employment discrimination. He oversaw the drafting of the landmark Civil Rights Act of 1968 — better known as the Fair Housing Act — which addressed housing discrimination. He sued to prevent discrimination in employment.

He also ordered a moratorium on federal executions and prison construction; banned wiretaps in criminal cases; and refused to enforce a law that was intended to countermand the Supreme Court’s restrictions on the questioning of criminal suspects under the so-called Miranda law.

Mr. Clark became such a liberal lightning rod that Richard M. Nixon, in his 1968 presidential campaign, repeatedly won applause by vowing to fire him. Indeed, Nixon had made him such an issue in the campaign that President Johnson blamed Mr. Clark, with whom he had had an almost fatherly relationship, for Nixon’s slim victory over the Democratic candidate, Vice President Hubert H. Humphrey.

After the election, Johnson stopped speaking to Mr. Clark and did not invite him to his final cabinet luncheon.