After working for many years as a reporter, Caro wrote The Power Broker (1974), a biography of New York urban planner Robert Moses, which was chosen by the Modern Library as one of the hundred greatest nonfiction books of the twentieth century.

Princeton in the mid-1950s was hardly known for being hospitable towards the Jewish community, and though Caro says he did not personally suffer from anti-Semitism, he saw plenty of students who did."

"[3] After briefly enrolling in the English doctoral program at Rutgers University, where he served as a teaching assistant, he spent six years as an investigative reporter with the Long Island newspaper Newsday.

An early article, "Anatomy of a $9 Burglary," investigating the lives of those affected by a theft of $9 from a Long Island home, was held by The New York Times as a strong example of Caro's ceaseless research process to uncover the deep truth behind a story.

'"[3] Caro gave a speech to introduce Senator Ted Kennedy on the second day of the 2004 Democratic National Convention, emphasizing the importance of courage in American leaders.

During the 1967–1968 academic year, Caro worked on the book as a Carnegie Fellow at the Columbia University Graduate School of Journalism.

[3] The Power Broker is widely viewed[13] as a seminal work because it combined painstaking historical research with a smoothly flowing narrative writing style.

The success of this approach was evident in his chapter on the construction of the Cross-Bronx Expressway, where Caro reported the controversy from all perspectives, including that of neighborhood residents.

The ex-president had recently died and Caro had already decided, before meeting with Gottlieb on the subject, to undertake his biography; he "wanted to write about power".

[17][18][19] It will cover Johnson and Vietnam, the Great Society and civil rights era, his decision not to run in 1968, and eventual retirement.

[22] Caro's books portray Johnson as a complex and contradictory character: at the same time a scheming opportunist and visionary progressive.

Caro's portrayal of Johnson also notes his struggles on behalf of progressive causes such as the Voting Rights Act, and his consummate skill in getting this enacted in spite of intense opposition from Southern Democrats.

[3] While writing the books, Caro read the works of the novelist Leo Tolstoy and the historian Edward Gibbon, alternating between the two.

"There's almost a view that if it's well written it can't be good history," he told Mark Rozzo of the Los Angeles Times in 2002.

[25] His 2019 book Working has been described as a "semi-memoir" focused on "Caro's selection of observations...on the arts of researching, interviewing and writing".

"[25][27] After conducting his years-long research, Caro attempts to "see the whole book right down to the last line," by putting up an outline on a 22-foot corkboard before writing the first manuscript, as a way to prevent writer's block.

[4] He writes several successive drafts in longhand on discontinued "legal pads, white with narrow lines," which Caro has mass-ordered and keeps in East Hampton.

[28] Subsequently, Caro types his books on Smith Corona Electra 210 typewriters, which The New Republic called "a model practically synonymous with him".

[29] One of these, the one used when writing The Power Broker, was placed on display in the New-York Historical Society's "Turn Every Page": Inside the Robert A. Caro Archive exhibition.

[28] Since Caro retypes several versions of his manuscripts before submitting them for publication, he prefers a bolder text, which he achieves by using cotton ribbon, instead of the now-common nylon.

As the former were discontinued, his wife Ina found a supplier that would manufacture them on the condition that Caro order a dozen gross, or 1,728 units.

[28] He edits with the use of red 314 Berol Draughting pencils and keeps "a ledger tracking how many words he has written against his stringent 1,000-word daily goal".

In October 2007, Caro was named a "Holtzbrinck Distinguished Visitor" at the American Academy in Berlin, Germany but then was unable to attend.

"[31] In 2011, Robert Caro was the recipient of the 2011 BIO Award given each year by members of Biographers International "to a colleague who had made a major contribution in the advancement of the art and craft of real life depiction".

She sold their house and took a job teaching school to fund work on The Power Broker and is the only other person who conducted research for his books.

[3][46][47] Caro's son, Chase, pled guilty to second-degree grand larceny in 2007 for stealing over $750,000 from three former clients in the course of real estate transactions.

[78] Motherless Brooklyn, the 2019 film directed by Edward Norton, loosely based on the 1999 novel of the same name by Jonathan Lethem, was inspired by Caro's biography of Robert Moses, The Power Broker.