Nathaniel Branden was born Nathan Blumenthal as the only boy in a family of sisters in Brampton, Ontario; his sister Elayne Blumenthal, a nurse, was part of the Ayn Rand "collective". Another family member, Allan Blumenthal, a cousin and a successful practicing psychiatrist, was also a member of "The Collective". Branden completed high school in Canada, his native country.

Branden received a BA in psychology from the University of California Los Angeles, an MA from New York University, and in 1973, a Ph.D. in psychology from the California Graduate Institute (CGI), then an unaccredited, state-approved school whose graduates may be licensed by the state to practice psychology. Graduates of unaccredited state-approved schools such as CGI are limited to associate membership in the American Psychological Association.

In 1950, after having become a fan of Ayn Rand's novels and exchanging letters and phone calls with her, the 19-year-old Branden met Rand. The pair went on to develop an eighteen-year personal and professional relationship. Eventually, Rand and the much younger Branden had a romantic affair. While both were married to other people at the time, both of their respective spouses consented to the affair before it started. According to Barbara Branden, however, "the affair was agonizingly painful," both to her and Rand's husband.

For many years Branden was considered to be a leading figure in the Objectivist movement; indeed, many perceived him as being second only to Rand herself. He was the leader of a group of Rand's closest associates known as The Collective, which also included his wife Barbara Branden, Leonard Peikoff and Alan Greenspan. At the time, Rand considered him to be a soul mate of hers and designated him her "intellectual heir." In 1958 Branden founded the Nathaniel Branden Institute to promote Objectivism through lectures and educational seminars around the United States. The NBI became enormously successful, and soon had representatives all over the US and around the world. During the period of her affair with Branden, Ayn Rand wrote Atlas Shrugged, which she considered to be her magnum opus. She named one of the minor characters in the book "Nathaniel" after Branden. He was a heroic 19th Century railroad builder, an ancestor of the book's main protagonist whom she seeks to emulate and whose picture she keeps on her wall throughout the book.

In 1965 Branden separated from his wife. In 1968, the close relationship between Rand and Branden came to an abrupt end when Rand discovered that Branden had been having a sexual relationship with a third woman, actress Patrecia Scott, without Rand's knowledge, for more than four years. While Rand had grown skeptical of Branden's feelings, she had also grown skeptical of his general intellectual "drift" along with the weakening commitment to Objectivism that Branden would admit to in later interviews. Rand then expelled Branden from the Objectivist movement. She published a letter in The Objectivist repudiating Branden for these reasons, including his dishonesty, but she did not mention their affair. Branden published a response in which he, too, did not disclose an affair, but in which he publicly accused Rand of desiring such an affair with him. He claimed that their age difference was "an insuperable barrier," for him, to such an affair. The two never reconciled, and Branden remained persona non grata to the mainline Objectivist movement, particularly the group that would go on to form the Ayn Rand Institute.

In 1989 Branden published his account of this time in his life. The memoir was entitled Judgment Day. Then in 1999, Branden re-published a revised edition, entitled My Years with Ayn Rand. Branden's account provides an inside view of Ayn Rand as a person, the development of Objectivism, its inner circle, and the tumultuous relationships between Ayn Rand and her associates. Branden supported David Kelley's notion of Objectivism as an "open system" in a 1999 article he wrote, "Who Owns Objectivism?" Branden has since rejected certain elements of the Objectivist philosophy, particularly what he considers its strictly cognitivist view of psychology, and his memoirs chronicle many of what he charges to be emotionally repressive elements of Rand, some of which he argues show up in her fiction. He has likewise argued that followers' obsession with Rand herself led to an unhealthy cult of personality within the movement, damaging the common sense of both Rand and other Objectivists. Branden has also been known to talk freely of his interest in matters that Rand would have considered epistemological "mysticism," such as ESP, and has had a publicized relationship with Ken Wilber. However, while Branden has claimed that Wilber is "one of the most brilliant minds I have ever encountered," he also states that "[i]f you are familiar with Ken's ideas, you know that he and I have our disagreements, much as I admire his work. Ken is a mystic. I am not."

Branden has retained his support for the fundamentals of the Objectivist ethics. In his book "Honoring the Self" (Branden, 1983), he devotes Chapter 12 to a defense of Ayn Rand's metaethical theory, saying that, "the foundation of her ethics is an unassailable contribution" (Branden 1983, p205).

As a psychologist Branden has elucidated the crucial role of self-esteem in psychological health, and has outlined the volitional practices he has observed to be essential to achieving and maintaining self-esteem. As a therapist, he developed a sentence completion test, a psychotherapeutic tool proposed as useful for making unconscious thoughts and feelings conscious, and to transform limiting beliefs and attitudes. Currently, he tends to use a blend of sentence completion exercises, exercises derived from energy therapy, humor, and "just plain talking" in his therapy practice. Nathaniel Branden continues to write and practice psychotherapy in Los Angeles, California, as well as present seminars and workshops on self-esteem.

California Assemblyman John Vasconcellos discovered self-esteem and became convinced it was the solution to many a social evil. Promoted by Assemblyman Vasconcellos, the state legislature of California formed "The California Task Force to Promote Self-Esteem and Personal and Social Responsibility." After some initial setbacks, including a veto by the governor, the legislation creating the 25-member task force was passed and signed into law in the Fall of 1986. One result of the California Task Force was the creation of NASE (National Association for Self-Esteem) "dedicated to integrating self-esteem into the fabric of American society." Nathaniel Branden is a member of the board. In its 1989 report, the state of California task force on self-esteem concluded: "... Many, if not all, the major problems plaguing society have roots in the low self-esteem of many of the people who make up society." According to some educational authorities, if Branden's concept of self-esteem had been accepted as he proposed as far back as 1969, it would have been a force for good in the field of education. Instead, there was only the acceptance of self-esteem simply as "having a favorable opinion of oneself" regardless of any objective evidence to the contrary. However, in the twenty first century, in 2003, the self-esteem movement suffered a serious setback when it was conclusively proven that in the relation between self-esteem and the education of children, the inculcation of self-esteem in children does not raise grades, better career achievements or produces any other positive effects in the field of education.

In the 1970s, Branden moved to California and married Patrecia Scott (a divorce with Barbara Branden having occurred before his break with Rand). In 1977, Scott unexpectedly died at home due to what was thought to be an epileptic seizure presumably triggered by sunlight off the water in the pool while feeding their dog. Branden married a third time in 1978, wedding businesswoman Devers Israel. They later divorced. He subsequently married his fourth wife, Leigh Horton. Branden retained a relationship...sometimes friendly, sometimes acrimonious...with his first wife, Barbara, who wrote a successful book, The Passion of Ayn Rand, which detailed Branden's relationship with Rand and the bitter breakup. The book was made into a motion picture in 1999 starring Helen Mirren as Rand and Eric Stoltz as Branden.

• Who Is Ayn Rand? (with Barbara Branden) (1962)
• The Psychology of Self-Esteem (1969)
• Breaking Free (1970)
• The Disowned Self (1971)
• The Psychology of Romantic Love (1980)
• The Romantic Love Question & Answer Book (with Devers Branden) (1982)
• Honoring the Self (1983)
• If You Could Hear What I Cannot Say (1985)
• How To Raise Your Self Esteem (1987)
• My Years with Ayn Rand (1989)
• The Power of Self-Esteem (1992)
• The Art of Self Discovery (1993)
• The Six Pillars of Self-Esteem (1994)
• Taking Responsibility (1996)
• The Art of Living Consciously (1997)
• A Woman's Self-Esteem (1998)
• Nathaniel Branden's Self-Esteem Every Day (1998)
• Self-Esteem at Work (1998)
• My Years with Ayn Rand (1999) (revised edition of Judgment Day)
• 32nd Anniversary Edition of Psychology of Self-Esteem (2001)
• The Vision of Ayn Rand (2009) (book version of his "Basic Principles of Objectivism" lecture series)

Branden's books have been translated into 18 languages, with more than 4 million copies in print. In addition, Branden contributed essays to two of Ayn Rand's essay collections, The Unknown Ideal and The Virtue of Selfishness.