Lasch came from a highly political family rooted in the left. His father, Robert Lasch, was a Rhodes Scholar and journalist; in St. Louis he won a Pulitzer prize for editorials criticizing the Vietnam War. Zora Lasch, his mother, who held a philosophy doctorate, worked as a social worker and teacher.

He studied at Harvard and Columbia, where he worked with William Leuchtenburg. He contributed a Foreword to later editions of Hofstadter's "The American Political Tradition" and an article on Hofstadter in the New York Review of Books in 1973.

Lasch taught at the University of Iowa and then was a professor of history at the University of Rochester from 1970 until his death from cancer in 1994.

He also took a conspicuous public role. Russell Jacoby acknowledged this in writing that "I do not think any other historian of his generation moved as forcefully into the public arena". In 1986 he appeared on BBC television in discussion with Michael Ignatieff and Cornelius Castoriadis.

During the 1960s, Lasch identified himself as a socialist, but one who found influence not just in the writers of the time such as C. Wright Mills but also in earlier independent voices such as Dwight Macdonald. Lasch became further influenced by writers of the Frankfurt School and the early New Left Review and felt that "Marxism seemed indispensable to me". During the 1970s, however, he became disenchanted with the Left's belief in progress and increasingly identified this belief as the factor which explained the Left's failure to thrive despite the widespread discontent and conflict of the times.

At this point Lasch began to formulate what would become his signature style of social critique - a syncretic synthesis of Freud and the strand of paleoconservative thinking that remained deeply suspicious of Capitalism and its effects on traditional institutions.

Besides Leuchtenburg, Hofstadter and Freud, Lasch was especially influenced by Orestes Brownson, Henry George, Lewis Mumford, Jacques Ellul, Reinhold Niebuhr, and Philip Rieff

Lasch's earliest argument, anticipated partly by Hofstadter's concern with the cycles of fragmentation among radical movements in the United States, was that American radicalism had at some point in the past become socially untenable. Members of "the Left" had abandoned their former commitments to economic justice and suspicion of power, to assume professionalized roles and to support commoditized lifestyles which hollowed out communities' self-sustaining ethics. His first major book, The New Radicalism in America: The Intellectual as a Social Type, published in 1965 (with a promotional blurb from Hofstadter), expressed those ideas in the form of a bracing critique of twentieth-century liberalism's efforts to accrue power and restructure society, while failing to follow up on the promise of the New Deal. Most of his books, even the more strictly historical ones, include such sharp criticism of the priorities of alleged "radicals" who represented merely extreme formations of a rapacious capitalist ethos.

Lasch's most famous work, The Culture of Narcissism (1979), sought to relate the hegemony of modern-day capitalism to an encroachment of a "therapeutic" mindset into social and family life similar to that already theorized by Philip Rieff. Lasch posited that social developments in the 20th century (e.g., World War II and the rise of consumer culture in the years following) gave rise to a narcissistic personality structure, in which individuals’ fragile self-concepts had led, among other things, to a fear of commitment and lasting relationships (including religion), a dread of aging (i.e., the 1960s and 1970s "youth culture") and a boundless admiration for fame and celebrity (nurtured initially by the motion picture industry and furthered principally by television). He claimed, further, that this personality type conformed to structural changes in the world of work (e.g., the decline of agriculture and manufacturing in the U.S. and the emergence of the "information age"). With those developments, he charged, inevitably there arose a certain therapeutic sensibility (and thus dependence) that, inadvertently or not, undermined older notions of self-help and individual initiative. By the 1970s even pleas for "individualism" were desperate and essentially ineffectual cries which expressed a deeper lack of meaningful individuality.

Most explicitly in The True and Only Heaven, Lasch developed a critique of social change among the middle classes in the U.S., explaining and seeking to counteract the fall of elements of "populism." He sought to rehabilitate this populist or producerist alternative tradition:

"The tradition I am talking about ... tends to be skeptical of programs for the wholesale redemption of society... It is very radically democratic and in that sense it clearly belongs on the Left. But on the other hand it has a good deal more respect for tradition than is common on the Left, and for religion too.

and said that

"...any movement that offers any real hope for the future will have to find much of its moral inspiration in the plebeian radicalism of the past and more generally in the indictment of progress, large-scale production and bureaucracy that was drawn up by a long line of moralists whose perceptions were shaped by the producers' view of the world"

By the 1980s, Lasch had poured scorn on the whole spectrum of contemporary mainstream American political thought, angering liberals with attacks on progressivism and feminism. Liberal journalist Susan Faludi dubbed him explicitly anti-feminist for his criticism of the abortion rights movement and opposition to divorce. But Lasch viewed Ronald Reagan's conservatism as the antithesis of tradition and moral responsibility. Lasch was not generally sympathetic to the cause of what was then known as the New Right, particularly those elements of libertarianism most evident in its platform; he detested the encroachment of the capitalist marketplace into all aspects of American life. Lasch rejected the dominant political constellation that emerged in the wake of the New Deal in which economic centralization and social tolerance formed the foundations of American liberal ideals, while also rebuking the diametrically-opposed synthetic conservative ideology fashioned by William F. Buckley, Jr. and Russell Kirk. Lasch also was surprisingly critical and at times dismissive toward his closest contemporary kin in social philosophy, communitarianism as elaborated by Amitai Etzioni. Only populism satisfied Lasch's criteria of economic justice (not necessarily equality, but minimizing class-based difference), participatory democracy, strong social cohesion and moral rigor; yet populism had made major mistakes during the New Deal and increasingly been co-opted by its enemies and ignored by its friends. For instance, he praised the early work and thought of Martin Luther King as exemplary of American populism; yet in Lasch's view, King fell short of this radical vision by embracing in the last few years of his life an essentially bureaucratic solution to ongoing racial stratification.