Lautenberg, who was the Senate's last remaining World War II veteran, had said in February he would not seek a sixth term next year, setting up a major battle for the seat.
Republican Senate majority leader Mitch McConnell called Lautenberg a "patriot whose success in business and politics made him a great American success story and a standout even within the fabled Greatest Generation."
"The entire Senate is saddened today," McConnell said in a statement.
He wrote the law that set the national legal drinking age at 21 and pushed legislation through Congress to reduce the blood alcohol limit that defined drunk driving.
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Lautenberg, the son of poor Russian and Polish Jewish immigrants, joined the US Army when he was 18 and served in Europe in the Army Signal Corps.
He graduated from Columbia University and eventually became a successful businessman before entering politics.
The race to fill his New Jersey seat will be among the most closely watched in 2014 elections, with the popular and charismatic Newark Mayor Cory Booker seen as a frontrunner.