Born in Brooklyn, Walter Pincus worked as a copyboy at the New York Times after graduating from Yale University. He was drafted into the U.S. Army in 1955 and served in the U.S. Army Counterintelligence Corps in Washington from 1955-1957. After his discharge, he worked on the copy desk of The Wall Street Journal's Washington edition. He left in 1959 to become Washington correspondent for three North Carolina newspapers. In 1963, he moved to the Washington Star before joining The Washington Post, where he worked from 1966 to 1969. From 1972 to 1975, he was executive editor of The New Republic. He covered the Watergate Senate hearings, the House impeachment hearings and the Watergate trial, writing articles for the magazine and op-ed pieces for The Washington Post. In 1975, he returned to The Washington Post to write for the national staff of the newspaper.

When he resumed writing for the newspaper, he also was permitted to work as a part time consultant to NBC News and later CBS News, developing, writing or producing television segments for network evening news, magazine shows and hour documentaries.

Pincus has taken two 18-month sabbaticals from journalism. Both were spent directing investigations for the Senate Foreign Relations Committee under its then-chairman, Sen. J. William Fulbright. The first was into foreign government lobbying (1962-63) and the second into U.S. military and security commitments abroad and their effect on U.S. foreign policy (1969-70). Both investigations led to legislation. The first in a revision of the Foreign Agents Registration Act; the second in a series of limiting amendments on defense appropriations bills that culminated in the Hatfield-McGovern legislation to end the Vietnam War.

At The Washington Post, Pincus has written about a variety of national news subjects ranging from nuclear weapons and arms control to political campaigns to the American hostages in Iran to investigations of Congress and the Executive Branch. For six years he covered the Iran-contra affair. He covered the intelligence community and its problems arising out of the case of confessed spy Aldrich H. Ames, allegations of Chinese espionage at the nuclear weapons laboratories.

Pincus has won several newspaper prizes including the George Polk Award in 1977 for stories in The Washington Post exposing the neutron warhead; the 1961 Page One award for magazine reporting in The Reporter, and a television Emmy for writing on the 1981 CBS News documentary series, Defense of the United States. In 1999 he was awarded the first Stewart Alsop Award given by the Association of Foreign Intelligence Officers for his coverage of national security affairs. In 2002 he was one of six Post reporters who won a Pulitzer Prize for National Reporting.