Sen. Frank Lautenberg (D-N.J.) said he will not run again for the Senate.
Lautenberg, 89, had previously said he would consider running again in 2014.
On Thursday, he told various media that he would instead dedicate the final two years of his term to passing new gun controls and environmental protections and creating jobs in New Jersey.
Lautenberg first served in the Senate from 1982-2000.
Two signature laws are called the "Lautenberg Amendment." One passed in 1990 facilitates refugee status for those fleeing religious persecution. Designed originally for Soviet Jews, it has since been used to assist refugees from Vietnam, Burma and Iran among other nations.
The other passed in 1996 bans the sale of guns to people convicted of domestic violence.
Lautenberg first retired in 2000, but was asked by Democrats to run again in 2002 after incumbent Robert Toricelli was forced to drop out because of scandal.
Lautenberg's announcement was met with "sadness" by the National Jewish Democratic Council.
"Jewish Democrats around the country will miss his stalwart support for the U.S.-Israel relationship and his leadership on progressive domestic policies supported by the vast majority of American Jews," it said.