He enlisted into the United States Army in 1943 where he served as an infantryman with the 104th Infantry Division, landing in Cherbourg, France in September 1944. He earned two Battle Stars as a Combat Infantryman. He was honorably discharged with the rank of Sergeant in 1946.
In that year, Koch began attending the New York University School of Law; that summer he also worked as a busboy in a hotel in the upstate New York spa town of Sharon Springs. He received his law degree in 1948, was admitted to the bar in 1949, and began to practice law.
Koch has said he began his political career as "just a plain liberal," with positions including opposing the Vietnam War and marching in the South for civil rights. He has traced the beginning of his rightward shift towards being a "liberal with sanity" to the controversy in 1973 around then-New York City Mayor John Lindsay's attempt to place a 3,000-person housing project in the middle of a middle-class community in Forest Hills, Queens. Congressman Koch met with residents of the community, most of whom were against the proposal. He was convinced by their arguments, and spoke out against the plan; this decision, he has said, shocked many of his political associates.
In mid-1976, he was threatened with murder by Uruguayan secret police. He would learn about those threats only after Orlando Letelier's carbombing in Washington D.C., September 1976, by Michael Townley, an American agent for DINA, the Chilean secret police, working for Operation Condor.
In 1977, Koch ran in the Democratic primary of the New York mayoral election against incumbent Abe Beame, Bella Abzug and Mario Cuomo, among others. Koch ran to the right of the other candidates, on a "law and order" platform. According to historian Jonathan Mahler, the blackout that happened in July of that year, and the subsequent rioting, helped catapult Koch and his message of restoring public safety to front-runner status. Koch also attributes some measure of credit for his victory to Rupert Murdoch's decision to have the New York Post endorse him in both the primary and the general election. Koch won the initial vote in the Democratic primary, as well as a runoff vote held between him and Cuomo. In the general election, also held in 1977, Koch beat Cuomo, who ran on the Liberal Party ticket, and Roy M. Goodman, running on the Republican ticket.
After winning the election, Koch resigned from Congress to become the 105th Mayor of New York City.
His catch-phrase as Mayor was "How'm I doing?" When walking down the street, he would often use that question as a greeting to the people he talked to.
As Mayor, Ed Koch is credited with restoring fiscal stability to the City of New York, and placing the City on a budget balanced according to generally accepted accounting principles (GAAP). He also established a merit selection system for Criminal and Family Court judges, and established extensive housing programs. He issued an executive order prohibiting all discrimination against homosexuals by City employees. A second executive order binding suppliers of the City to the same standards was eventually struck down by court order insofar as it applied to religious organizations, which were exempted from civil rights legislation by State law. John Cardinal O'Connor and the Roman Catholic Archdiocese of New York were participants in the lawsuit against the executive order.
In April 1980, he successfully broke a strike by the city's subway and bus operators, invoking the state's Taylor Law, which prohibits strikes by state or local government employees and imposes fines on any union authorizing such a strike that steadily escalate each day the strike continues. On one morning he famously walked to City Hall across the Brooklyn Bridge, in solidarity with the many commuters who had chosen to walk to work. The strikers returned to work after eleven days.
He was a delegate to the 1980 Democratic National Convention from the city. However, he invited Ronald Reagan to Gracie Mansion shortly before that year's Presidential election, in which Reagan defeated Democratic incumbent Jimmy Carter — a move widely seen as a tacit endorsement of Reagan on the part of Koch.
In 1981, City College of New York awarded Koch a B.A. degree.
In 1982, Koch ran unsuccessfully for Governor of New York, losing the Democratic primary to Cuomo, who was then lieutenant governor. Many say the deciding factor in his loss was an interview with Playboy magazine in which he described the lifestyle of both suburbia and upstate New York as "sterile" and lamented the thought of having to live in "the small town" of Albany as Governor, turning off voters from outside the city.
Koch often deviated from the conventional liberal line, strongly supporting the death penalty and taking a hard line on "quality of life" issues, such as giving police broader powers in dealing with the homeless and favoring (and signing) legislation banning the playing of radios on subways and buses. These positions prompted harsh criticism of him from the local chapter of the American Civil Liberties Union and many African-American leaders, particularly the Reverend Al Sharpton.
In 1986, Mayor Koch signed a lesbian and gay rights ordinance for the city after the City Council passed the measure (on March 20), following several failed attempts by that body to approve such legislation. Despite his overall pro-lesbian and pro-gay-rights stance, he nonetheless backed up the New York City Health Department's decision to shut down the city's gay bathhouses in 1985 in response to concerns over the spread of AIDS. The enactment of the measure the following year placed the city in a dilemma, as it apparently meant that the bathhouses would have to be re-opened because many heterosexual "sex clubs" — most notably Plato's Retreat — were in operation in the city at the time, and allowing them to remain open while keeping the bathhouses shuttered would have been a violation of the newly-adopted anti-discrimination law. The Health Department, with Koch's approval, reacted by ordering the heterosexual clubs, including Plato's Retreat, to close as well (Plato's Retreat then moved to Fort Lauderdale, Florida, where it reopened under the new name Plato's Repeat).
Koch consistently demonstrated a fierce love for New York City, which some observers felt he carried to extremes on occasion: In 1984 he had gone on record as opposing the creation of a second telephone area code for the city, claiming that this would divide the city's population; and when the National Football League's New York Giants won the Super Bowl in January 1987, he refused to grant a permit for the team to hold their traditional victory parade in the city, quipping famously, "If they want a parade, let them parade in front of the oil drums in Moonachie" (the latter being a town in New Jersey adjacent to East Rutherford, site of the Meadowlands Sports Complex, where the Giants play their home games).
In his third term, his popularity was shaken after the Donald Manes suicide and the PVB scandal, even though Koch himself was not part of the corruption ring, and corruption involving associate Stanley Friedman.
Shortly afterwards Koch suffered a stroke in 1987 while in office, but was able to continue with his duties.
Koch became a controversial figure in the 1988 presidential campaign with his very public criticism of Democratic candidate Jesse Jackson, who had surprised many political observers by winning key primaries in March and running even with the front runner, Massachusetts Governor Michael Dukakis. As the April New York primary approached, Koch reminded voters of Jackson’s alleged anti Semitism and said that Jews would be "crazy" to vote for Jackson. Koch endorsed Tennessee Senator, Al Gore, who had run well in his native south, but hadn't won 20% in a northern state. As Koch's anti Jackson rhetoric intensified, Gore seemed to shy away from Koch. On primary day, Gore finished a weak third place with 10% of the vote and dropped out of the race. Jackson ran ten points behind Dukakis, whose nomination became inevitable after his NY win.
In 1989, he ran for a fourth term as Mayor but lost the Democratic primary to David Dinkins, who went on to defeat Rudolph Giuliani in the general election. Koch's anti-Jackson campaign in '88 had angered many black voters, likely playing a major role in Koch's defeat.
Koch had a minor heart attack in March 1999.
In 2004, together with his sister Pat Koch Thaler, Koch wrote a children's book, Eddie, Harold's Little Brother. From 2005 to 2007, Koch wrote a weekly column for the New York Press. He also writes film reviews for the Greenwich Village newspaper The Villager.
The former mayor occasionally appears in television specials and commercials that promote or advertise things about New York, such as commercials for Snapple (with the tagline "the best thing to ever come out of New York") and FreshDirect, a New York-based delivery service. He also made cameo appearances as himself in the movies Up At Lou's Fish (a documentary about the last days of the Fulton Fish Market), The Hebrew Hammer, We Own the Night and Eddie, and an episode of HBO's Sex and the City entitled The Real Me.
In April 2008, Koch announced that he had secured a burial plot in Manhattan's non-denominational Trinity Cemetery, stating that “the idea of leaving Manhattan permanently irritates me,” and that he hoped not to use the plot "for another 8-10 years." For the inscription on his memorial stone, Koch has requested that the marker will bear the Star of David and a Hebrew prayer, "Hear O Israel, the Lord our God, the Lord is One." It also will be inscribed with the last words of journalist Daniel Pearl before he was murdered by terrorists in 2002: "My father is Jewish. My mother is Jewish. I am Jewish. Koch explained that he had been moved that Pearl chose to affirm his faith and heritage in his last moments.
Though Koch supported Giuliani's first mayoral bid, he became opposed to him in January, 1996, and began writing a series of columns in the New York Daily News criticizing Giuliani, most frequently accusing him of being authoritarian and insensitive. In 1999, the columns were compiled into the book Giuliani: Nasty Man. He resumed his attacks, and had the book re-published, in 2007, after Giuliani announced his candidacy for President. In May 2007, Koch called Giuliani "a control freak" and said that he "wouldn't meet with people he didn't agree with... That's pretty crazy." He also said that Giuliani "was imbued with the thought that if he was right, it was like a God-given right. That's not what we need in a president.
Koch originally endorsed Hillary Clinton for the Democratic nomination for President during the 2008 presidential campaign, then endorsed Democratic nominee Barack Obama in the general election. In his endorsement of Obama, Koch wrote that he felt that (unlike in 2004) both sets of candidates would do their best to protect both the United States and Israel from terrorist attacks, but that he agreed with much more of Obama's domestic policies, and that the concept of Republican vice-presidential nominee Sarah Palin ascending to the presidency "would scare me".
Koch was an early supporter of the Iraq War. In July 2007, Koch wrote that he was "bailing out" of his previous support for that war, due to the failure of the United States' NATO allies, and other Arab countries, to contribute to the war effort. Koch wrote, "I would support our troops remaining in Iraq if our allies were to join us. But they have made it clear they will not." He added that the U.S. must still "prepare for the battles that will take place on American soil by the Islamic forces of terror who are engaged in a war that will be waged by them against Western civilization for at least the next 30 years.
Koch has generally been less explicit in his denials in later life, and refused comment on his actual sexual experiences, writing "What do I care? I'm 73 years old. I find it fascinating that people are interested in my sex life at age 73. It's rather complimentary! But as I say in my book, my answer to questions on this subject is simply 'Fuck off.' There have to be some private matters left." Randy Shilts, in And the Band Played On, his influential history of the early AIDS epidemic in America, discusses the possibility that Koch ignored the developing epidemic in New York City in 1982–1983 because he was afraid of lending credence to rumors of his homosexuality. Author and Activist Larry Kramer has been more pointed in his criticism of Koch. He describes the former mayor as a "closeted gay man" whose fear of being 'outed' kept him from aggressively addressing the AIDS epidemic in New York City in the early 1980s.