Branden was born in 1930 with the name Nathan Blumenthal in Brampton, Ontario, Canada. He received a BA in psychology from the University of California Los Angeles. He received a Ph.D. in psychology from New York University.

Biography
In 1950, after having exchanged letters and phone calls, 19-year-old Branden met novelist-philosopher Ayn 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, despite both being married (they first sought the consent of their spouses).

For many years Branden was considered to be the leading figure in the Objectivist movement, 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 and Alan Greenspan. Rand considered him to be her soul mate and designated him her "intellectual heir". In the late 50's Branden founded the Nathaniel Branden Institute to promote Objectivism through guest lectures and educational seminars around the United States. The NBI became enormously successful, and soon expanded to offices all over the US and around the world.

In 1968, the close relationship between Rand and Branden came to an abrupt end when Rand discovered that Branden was having a sexual relationship with a third woman, actress Patrecia Scott. Rand then expelled Branden from the Objectivist movement. In a public announcement, she did not mention the relationship as such, but cited his alleged misuse of funds among other factors in the decision.

Branden subsequently admitted to behaving "irrationally" though in his memoirs he would later admit that he considered Rand's move a hysterical over-reaction. The two never reconciled, and Branden remained a persona non grata in the Objectivist movement. Shortly thereafter Branden moved from New York to California and married Patrecia Scott (a divorce with Barbara having occurred before his break with Ayn). Scott died in a freak accident in 1977, and Branden married a third time in 1978, wedding businesswoman Devers Israel.

Post Objectivist Career
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 has since rejected certain elements of the Objectivist philosophy, particularly its cognitivist view of psychology, and his memoirs chronicle many of the emotionally repressive elements of Rand, some of which he argues show up in her fiction. He 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.

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, Branden developed the sentence completion method, a powerful and sophisticated psychotherapeutic tool that can be used both to make unconscious thoughts and feelings conscious, and to transform limiting beliefs and attitudes.

Politically, Branden has retained most of his strict capitalist politicial views, though some of these have evolved since the split with Rand: for example, unlike Rand, he says he "will leave the door open for emergency situations that I just can’t imagine being resolved in a free market context [like natural disasters and epidemics]. If they could be, then they should be. But the fact of emergencies should not be made as justification for violating individual rights, so as you can see, it’s a very tiny difference." In addition to changing his views on Objectivism, he now views Objectivists differently: "Philosophical principles are no substitute for thinking, yet many Objectivists act as if they were."

Nathaniel Branden continues to write and practice psychotherapy in Los Angeles, California, as well as present seminars and workshops on self-esteem. He is affiliated with the United States Libertarian Party, though he was unenthusiastic about it in the 2004 election. Most "orthodox" Objectivists like those at the Ayn Rand Institute oppose libertarianism outright.