Whitney North Seymour Jr., a patrician Republican who battled graft as President Richard M. Nixon’s United States attorney in Manhattan in the 1970s, and as a special prosecutor later won a perjury case against a former senior aide to President Ronald Reagan, died on Saturday in Torrington, Conn. He was 95.

Mr. Seymour died at Charlotte Hungerford Hospital, his brother, Thaddeus, said.

Prominent in New York civic, social and legal circles, the scion of a lawyer who championed unpopular causes and served in the Hoover administration, Mr. Seymour was elected to two terms in the New York State Senate in the 1960s, although his political career fizzled with losses in a race for Congress in 1968 and a run for the United States Senate in 1982.

But he made his name as a prosecutor. From 1970 to 1973, he was the United States attorney for the Southern District of New York, the Justice Department’s most prestigious outpost, which at that time included Manhattan, the Bronx and nine upstate counties. He replaced Robert M. Morgenthau, a Democrat who was forced out after nine years and became a popular Manhattan district attorney.

Mr. Seymour won convictions of Wall Street felons, organized crime leaders and narcotics traffickers, as well as high-profile corruption cases against former State Senator Seymour R. Thaler; Martin Sweig, an aide to Speaker John W. McCormack; and Robert T. Carson, a senior assistant to Senator Hiram L. Fong of Hawaii.