Plato Cacheris, the Washington lawyer of choice for accused spies, wayward sheikhs and notorious figures in scandals, from the Watergate affair to the sexual peccadilloes of President Bill Clinton, died on Thursday at a rehabilitation center in Alexandria, Va . He was 90.

The cause was complications of pneumonia, his daughter, Lisa Burnett, said.

Mr. Cacheris (pronounced ka-CHAIR-ess) specialized in cases that captivated the nation, including those of Robert Philip Hanssen and Aldrich Ames, who were convicted of spying for the Soviet Union and Russia , and Edward J. Snowden, the National Security Agency contractor who illegally disclosed troves of national secrets to journalists and found safe haven in Moscow.

Victory, to Mr. Cacheris, often did not mean acquittal. For Mr. Hanssen and Mr. Ames, who faced the death penalty for espionage, it meant life sentences negotiated by their lawyer in plea deals with prosecutors. For Mr. Snowden, who retained Mr. Cacheris in 2013 after being charged with espionage, it has meant exile in Russia, out of reach of prosecutions and prison in America.

And for clients like Monica Lewinsky, Mr. Clinton’s Oval Office mistress, and Fawn Hall, the National Security Council secretary who shredded documents for her boss, Lt. Col. Oliver North, in the Iran-contra scandal during the Reagan administration, the arrangements meant freedom from prosecution in exchange for their testimony.