Jeff Bell, 74, a three-time Republican U.S. Senate candidate in New Jersey who was an influential voice in the conservative movement, died Saturday night, Feb. 10. The cause of death wasn't immediately known.

Mr. Bell was a campaign aide to former President Richard M. Nixon and a speechwriter for Ronald Reagan during his unsuccessful 1976 primary challenge to President Gerald R. Ford.

"He was a kind and generous man with an original mind, a fighting spirit, and a deep faith," William Kristol, the conservative commentator and a friend, wrote Sunday on Twitter.

Mr. Bell, an Army veteran who served in Vietnam, made his own foray into electoral politics, shocking the New Jersey political establishment in 1978 by winning the Republican primary against incumbent U.S. Sen. Clifford Case. Mr. Bell then lost in the general election to Democrat Bill Bradley.

Mr. Bell again ran for Senate in 1982, but this time lost in the primary. He moved to Virginia and influenced policy debates in Washington. In 2009, he co-founded the American Principles Project, a nonprofit that "works to advance human dignity through public policy."

"Jeff Bell left a mark on everyone who knew him. His influence in the conservative movement — as an advocate for supply-side economics and social conservatism, as a policy staffer for Ronald Reagan, and as a three-time candidate for Senate in New Jersey — is well-known," Frank Cannon, president of the American Principles Project, based in Washington, said in a statement Monday.

Returning to New Jersey in 2014, Mr. Bell won the Republican nomination for U.S. Senate for the second time. Running against Democratic Sen. Cory A. Booker, Mr. Bell campaigned on a pledge to rein in the Federal Reserve and return U.S. monetary policy to the gold standard. Booker won the election.

Mr. Bell lived in Annandale, Va., and had a residence in Leonia, N.J., according to a spokesman for the American Principles Project.

He is survived by his wife, Rosalie, and children Jimmy, Nicky, Julia, and Damien.