Lieberman was born in Stamford, Connecticut, the son of Henry, who ran a liquor store, and Marcia (nee Manger) Lieberman. His family is Jewish; his paternal grandparents emigrated from Congress Poland and his maternal grandparents were from Austria-Hungary. He received a B.A. in both political science and economics from Yale University in 1964 and was the first member of his family to graduate from college. At Yale he was editor of the Yale Daily News and a member of the Elihu Club.

Lieberman was one of the Senate's strongest advocates for the war in Iraq. He is also an outspoken supporter of the U.S.-Israel relationship. On domestic issues, he strongly supports free trade economics while reliably voting for pro-trade union legislation. He has also opposed filibustering Republican judicial appointments. With Lynne Cheney and others, Lieberman co-founded American Council of Trustees and Alumni in 1995. Lieberman is a supporter of abortion rights and of the rights of gays and lesbians to adopt children, to be protected with hatecrime legislation, and to serve openly in the military. Lieberman was one of the Senate's leading opponents of violence in video games and on television. Lieberman describes himself as being "genuinely an Independent," saying "I agree more often than not with Democrats on domestic policy. I agree more often than not with Republicans on foreign and defense policy." Lieberman is also famous for championing, authoring and leading the effort that led to the repeal of Don't ask, don't tell.  During debate on the Patient Protection and Affordable Care Act, Lieberman opposed the public option. As the crucial 60th vote needed to pass the legislation, his opposition to the public option was critical for its removal from the resulting bill.  Lieberman was an integral part in attempting to stop WikiLeaks from publishing further material using U.S.-based corporations in the United States diplomatic cables leak of 2010.  In June 2015, Lieberman was a signatory to a public letter written by a bipartisan group of 19 U.S. diplomats, experts, and others, on the then-pending negotiations for an agreement between Iran and world powers over Iran's nuclear program. That letter outlined concerns about several provisions in the then-unfinished agreement and called for a number of improvements to strengthen the prospective agreement and win the letter-writers' support for it. The final agreement, concluded in July 2015, shows the influence of the letter.  On May 17, 2017, it was reported that Lieberman was a frontrunner to replace FBI Director James Comey, who was fired by President Donald Trump on May 9, 2017.

Did he do anything else to show his opposition to Iran?
signatory to a public letter written by a bipartisan group of 19 U.S. diplomats, experts, and others, on the then-pending negotiations for an agreement between Iran