"I am proud to endorse Senator Clinton and bring real change to America," Menendez said in an announcement in Washington, D.C. "As someone who voted against the Iraq war, Senator Clinton is the one to get us out of this war."
Menendez also said Clinton laid the path toward embracing universal health care. He spoke in Spanish to add that "it's a time to reform immigration and we need a person in the White House who looks out for our interests."
President Bush has been a vocal supporter of immigration reform that allows illegals a path to legal worker status and creates a guest worker program, but all the Republican presidential candidates save Arizona Sen. John McCain have opposed the immigration reforms now being considered by the Senate.
Clinton said she was deeply honored and moved to receive Menendez' endorsement.
"Together we are fighting to fix our immigration system. ... We cannot turn our backs on families and we will not give up," she said noting that her campaign manager is Latina. "Every vote is important to me ... Latino support is especially important to me."
Menendez noted that both Clinton and Sen. Barack Obama campaigned for him during his senatorial campaign last fall. He said he notified Obama on Monday that he would be endorsing Clinton.
FOX News' Jake Gibson contributed to this report.